Current Electricity Online Test 12th Science
Current Electricity Online Test 12th Science
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- Review
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Question 1 of 104
1. Question
Which among the following constitutes motion of charges?
Correct
The motion of charges constitutes ‘electric current’. In reality, the charges are always moving within the materials. For example, the electrons in a copper wire are never at rest and are continuously in random motion. Therefore, it is important to analyse the behaviour of charges when they are in motion.
Incorrect
The motion of charges constitutes ‘electric current’. In reality, the charges are always moving within the materials. For example, the electrons in a copper wire are never at rest and are continuously in random motion. Therefore, it is important to analyse the behaviour of charges when they are in motion.
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Question 2 of 104
2. Question
Current electricity owes its origin to whom?
Correct
Current electricity is the study of flow of electric charges. It owes its origin to Alessandro Volta (1745-1827), who invented the electric battery which produced the first steady flow of electric current. Modern world depends heavily on the use of electricity. It is used to operate machines, communication systems, electronic devices, home appliances etc., In this unit, we will study about the electric current, resistance and related phenomenon in materials.
Incorrect
Current electricity is the study of flow of electric charges. It owes its origin to Alessandro Volta (1745-1827), who invented the electric battery which produced the first steady flow of electric current. Modern world depends heavily on the use of electricity. It is used to operate machines, communication systems, electronic devices, home appliances etc., In this unit, we will study about the electric current, resistance and related phenomenon in materials.
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Question 3 of 104
3. Question
Which among the following statement is correct
1) Atom is made up of matters. Each atom consists of a negatively charged electrons with positively charged nucleus moving around. Atoms in metals have one or more electrons which are loosely bound to the nucleus. These electrons are called valid electrons and can be easily detached from the atoms.
2) The substances which have an abundance of these free electrons are called conductors. These free electrons move randomly throughout the conductor at a given temperature. In general due to this random motion, there is no net transfer of charges from one end of the conductor to other end and hence no current in the conductor.
3) When a potential difference is applied by the battery across the ends of the conductor, the free electrons drift towards the positive terminal of the battery, producing a net electric current.Correct
Matter is made up of atoms. Each atom consists of a positively charged nucleus with negatively charged electrons moving around the nucleus. Atoms in metals have one or more electrons which are loosely bound to the nucleus. These electrons are called free electrons and can be easily detached from the atoms.
Incorrect
Matter is made up of atoms. Each atom consists of a positively charged nucleus with negatively charged electrons moving around the nucleus. Atoms in metals have one or more electrons which are loosely bound to the nucleus. These electrons are called free electrons and can be easily detached from the atoms.
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Question 4 of 104
4. Question
Which among the following statement is correct?
Correct
We know that the mass move from higher gravitational potential to lower gravitational potential. Likewise, positive charge flows from region of higher electric potential to region of lower electric potential and negative charge flows from region of lower electric potential to region of higher electric potential. So, battery or electric cell simply creates potential difference across the conductor.
Incorrect
We know that the mass move from higher gravitational potential to lower gravitational potential. Likewise, positive charge flows from region of higher electric potential to region of lower electric potential and negative charge flows from region of lower electric potential to region of higher electric potential. So, battery or electric cell simply creates potential difference across the conductor.
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Question 5 of 104
5. Question
Which in a conductor is defined as the rate of flow of charges through a given cross-sectional area A?
Correct
The electric current in a conductor is defined as the rate of flow of charges through a given cross-sectional area A.
Incorrect
The electric current in a conductor is defined as the rate of flow of charges through a given cross-sectional area A.
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Question 6 of 104
6. Question
If a net charge Q passes through any cross section of a conductor in time t, then the current is defined as _____
Correct
If a net charge Q passes through any cross section of a conductor in time t, then the current is defined as I = Q / t. But charge flow is not always constant. Hence current can more generally be defined as Iavg = ΔQ/ Δt.
Incorrect
If a net charge Q passes through any cross section of a conductor in time t, then the current is defined as I = Q / t. But charge flow is not always constant. Hence current can more generally be defined as Iavg = ΔQ/ Δt.
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Question 7 of 104
7. Question
Compute the current in the wire if a charge of 120 C is flowing through a copper wire in 1 minute?
Correct
The current (rate of flow of charge) in the wire is I = Q / t = 120 / 60 = 2A.
Incorrect
The current (rate of flow of charge) in the wire is I = Q / t = 120 / 60 = 2A.
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Question 8 of 104
8. Question
Which among the following statement is correct regarding conventional current?
- In an electric circuit, arrow heads are used to indicate the direction of flow of current. By convention, this flow in the circuit should be from the positive terminal of the battery to the negative terminal. This current is called the conventional current or simply current and is in the direction in which a positive test charge would move.
- In typical circuits the charges that flow are actually electrons, from the negative terminal of the battery to the positive terminal. As a result, the flow of electrons and the direction of conventional current point in opposite direction. Mathematically, a transfer of positive charge is the same as a transfer of negative charge in the opposite direction.
Correct
Incorrect
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Question 9 of 104
9. Question
Which produces enormous electric current in a short time in Nature?
Correct
Electric current is not only produced by batteries. In nature, lightning bolt produces enormous electric current in a short time. During lightning, very high potential difference is created between the clouds and ground and hence charges flow between the clouds and ground.
Incorrect
Electric current is not only produced by batteries. In nature, lightning bolt produces enormous electric current in a short time. During lightning, very high potential difference is created between the clouds and ground and hence charges flow between the clouds and ground.
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Question 10 of 104
10. Question
Which among the following statement is correct
- In a conductor the charge carriers are free electrons. These electrons move freely through the conductor and collide repeatedly with the negative ions. If there is electric field, the electrons move in random directions, and hence their velocities are also randomly oriented.
- On an average, the number of electrons travelling in any direction will be equal to the number of electrons travelling in the opposite direction. As a result, there is no net flow of electrons in any direction and hence there will not be any current. Suppose, a potential difference is set across the conductor by connecting a battery, an electric field is created in the conductor.
- This electric field exerts a force on the electrons, producing a current. The electric field accelerates the electrons, while ions scatter the electrons and change their direction of motion. Thus, we see zigzag motion of electrons. In addition to the zigzag motion due to the collisions, the electrons move slowly along the conductor in a direction opposite to that of
Correct
In a conductor the charge carriers are free electrons. These electrons move freely through the conductor and collide repeatedly with the positive ions. If there is no electric field, the electrons move in random directions, and hence their velocities are also randomly oriented.
Incorrect
In a conductor the charge carriers are free electrons. These electrons move freely through the conductor and collide repeatedly with the positive ions. If there is no electric field, the electrons move in random directions, and hence their velocities are also randomly oriented.
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Question 11 of 104
11. Question
Which is the average velocity acquired by the electrons inside the conductor when it is subjected to an electric field?
Correct
The drift velocity is the average velocity acquired by the electrons inside the conductor when it is subjected to an electric field.
Incorrect
The drift velocity is the average velocity acquired by the electrons inside the conductor when it is subjected to an electric field.
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Question 12 of 104
12. Question
The average time between two successive collisions is called _____
Correct
The average time between two successive collisions is called the mean free time denoted by τ. The acceleration r a experienced by the electron in an electric field is given by
Incorrect
The average time between two successive collisions is called the mean free time denoted by τ. The acceleration r a experienced by the electron in an electric field is given by
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Question 13 of 104
13. Question
Which among the following equation gives drift velocity?
Correct
The drift velocity vd is given by vd = a τ.
vd = E = −µE
Incorrect
The drift velocity vd is given by vd = a τ.
vd = E = −µE
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Question 14 of 104
14. Question
Which is defined as the magnitude of the drift velocity per unit electric field?
Correct
Here µ = e τ / m is the mobility of the electron and it is defined as the magnitude of the drift velocity per unit electric field.
µ = vd / E
Incorrect
Here µ = e τ / m is the mobility of the electron and it is defined as the magnitude of the drift velocity per unit electric field.
µ = vd / E
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Question 15 of 104
15. Question
What is the SI unit of mobility?
- m2 V s
- m2 V s-1
- m2 V-1 s-1
- m2 V-2 s-1
Correct
The SI unit of mobility is m2 V-1 s-1
Incorrect
The SI unit of mobility is m2 V-1 s-1
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Question 16 of 104
16. Question
The typical drift velocity of electrons in the wire is _____
- 10–4 m s–2
- 10–4 m s–1
- 20–2 m s–1
- 10–2 m s–1
Correct
The typical drift velocity of electrons in the wire is 10–4 m s–1
Incorrect
The typical drift velocity of electrons in the wire is 10–4 m s–1
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Question 17 of 104
17. Question
If an electric field of magnitude 570 N C–1, is applied in the copper wire, find the acceleration experienced by the electron?
- a = 1.001 × 1010 m s–1
- a = 2.001 × 1010 m s–2
- a = 1.001 × 1014 m s–2
- a = 2.001 × 1018 m s–2
Correct
E = 570 N C–1, e = 1.6 × 10–19 C, m = 9.11 × 10–31 kg
F = ma = eE
a = eE / m = (570 × 1.6 × 10–19) / 9.11 × 10–31
= 912 × 10–19 × 1031 / 9.11
a = 1.001 × 1014 m s–2
Incorrect
E = 570 N C–1, e = 1.6 × 10–19 C, m = 9.11 × 10–31 kg
F = ma = eE
a = eE / m = (570 × 1.6 × 10–19) / 9.11 × 10–31
= 912 × 10–19 × 1031 / 9.11
a = 1.001 × 1014 m s–2
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Question 18 of 104
18. Question
Which among the following statement is correct regarding Microscopic model of current?
- Consider a conductor with area of cross section A and let an electric field E be applied to it from right to left. Suppose there are n electrons per unit volume in the conductor and assume that all the electrons move with the same drift velocity vd
- The drift velocity of the electrons = vd. If the electrons move through a distance dx within a small interval of dt, then vd = dx/dt; dx = vd dt [Eqn 1]. Since A is the area of cross section of the conductor, the electrons available in the volume of length dx is = volume × number of electrons per unit volume = Adx × n [Eqn 2]
- By substituting dx from equation 1 in 2 we get = (A vd dt) n. Total charge in the volume element dQ = (charge) × (number of electrons in the volume element). dQ = (e)(Avd dt)n. Hence the current I = dQ / d. I = n e A vd.
Correct
Incorrect
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Question 19 of 104
19. Question
Which is defined as the current per unit area of cross section of the conductor?
Correct
The current density ( J ) is defined as the current per unit area of cross section of the conductor.
J = I / A = (n e A vd) / A
J = n e vd
Incorrect
The current density ( J ) is defined as the current per unit area of cross section of the conductor.
J = I / A = (n e A vd) / A
J = n e vd
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Question 20 of 104
20. Question
What is the SI unit of current density?
- A m–2
- A m–1
- A m
- A–1 m–1
Correct
The S.I unit of current density is A / m2 (or) A m–2
Incorrect
The S.I unit of current density is A / m2 (or) A m–2
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Question 21 of 104
21. Question
In general, the current density is a vector quantity and it is given by J = n e vd. But conventionally, we take the direction of (conventional) current density as the direction of electric field. So the equation becomes _____
Correct
In general, the current density is a vector quantity and it is given by J = n e vd. But conventionally, we take the direction of (conventional) current density as the direction of electric field. So the equation becomes J = σ E.
Incorrect
In general, the current density is a vector quantity and it is given by J = n e vd. But conventionally, we take the direction of (conventional) current density as the direction of electric field. So the equation becomes J = σ E.
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Question 22 of 104
22. Question
Which among the following equation is called conductivity
Correct
The equation σ = (n e2 τ) / m is called conductivity.
Incorrect
The equation σ = (n e2 τ) / m is called conductivity.
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Question 23 of 104
23. Question
The inverse of conductivity is called _____
Correct
The inverse of conductivity is called resistivity (ρ). Ρ = 1 / σ = m / (n e2 τ).
Incorrect
The inverse of conductivity is called resistivity (ρ). Ρ = 1 / σ = m / (n e2 τ).
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Question 24 of 104
24. Question
A copper wire of cross-sectional area 0.5 mm2 carries a current of 0.2 A. If the free electron density of copper is 8.4 × 1028 m–3 then compute the drift velocity of free electrons?
- vd = 0.03 × 10–3 m s–1
- vd = 0.06 × 10–3 m s–1
- vd = 0.09 × 10–3 m s–1
- vd = 1.2 × 10–3 m s–1
Correct
The relation between drift velocity of electrons and current in a wire of cross-sectional area A is
vd = I / neA = 0.2 / (8.4 × 1028 × 1.6 × 10−19 × 0.5 × 10−6)
vd = 0.03 × 10–3 m s–1.
Incorrect
The relation between drift velocity of electrons and current in a wire of cross-sectional area A is
vd = I / neA = 0.2 / (8.4 × 1028 × 1.6 × 10−19 × 0.5 × 10−6)
vd = 0.03 × 10–3 m s–1.
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Question 25 of 104
25. Question
Which among the following statement is correct
Correct
In general, the current I is defined as the scalar product of the current density and area vector in which the charges cross. Current density is a vector but current is a scalar. The current I can be positive or negative depending on the choice of the unit vector normal to the surface area A.
Incorrect
In general, the current I is defined as the scalar product of the current density and area vector in which the charges cross. Current density is a vector but current is a scalar. The current I can be positive or negative depending on the choice of the unit vector normal to the surface area A.
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Question 26 of 104
26. Question
Determine the number of electrons flowing per second through a conductor, when a current of 32 A flows through it?
- n = 2 × 1010 electrons
- n = 2 × 1020 electrons
- n = 4 × 1010 electrons
- n = 4 × 1020 electrons
Correct
I = 32 A, t = 1 s
Charge of an electron, e = 1.6 × 10–19 C
The number of electrons flowing per second, n =?
I = q / t = ne / t
n = It / e = 32 ×1/ (1.6 × 10–19) = 20 × 1019 = 2 × 1020 electrons.
Incorrect
I = 32 A, t = 1 s
Charge of an electron, e = 1.6 × 10–19 C
The number of electrons flowing per second, n =?
I = q / t = ne / t
n = It / e = 32 ×1/ (1.6 × 10–19) = 20 × 1019 = 2 × 1020 electrons.
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Question 27 of 104
27. Question
The ohm’s law can be derived from which among the following equation?
Correct
The ohm’s law can be derived from the equation J = σ E. Consider a segment of wire of length l and cross-sectional area A. When a potential difference V is applied across the wire, a net electric field is created in the wire which constitutes the current in the wire. For simplicity, we assume that the electric field is uniform in the entire length of the wire, then the potential difference (voltage V) can be written as V = El.
Incorrect
The ohm’s law can be derived from the equation J = σ E. Consider a segment of wire of length l and cross-sectional area A. When a potential difference V is applied across the wire, a net electric field is created in the wire which constitutes the current in the wire. For simplicity, we assume that the electric field is uniform in the entire length of the wire, then the potential difference (voltage V) can be written as V = El.
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Question 28 of 104
28. Question
Which among the following quantity is called resistance of the conductor?
Correct
The quantity 1 / σ A is called resistance of the conductor and it is denoted as R. The resistance is directly proportional to the length of the conductor and inversely proportional to area of cross section. Therefore, the macroscopic form of ohm’s law can be stated as V = I R.
Incorrect
The quantity 1 / σ A is called resistance of the conductor and it is denoted as R. The resistance is directly proportional to the length of the conductor and inversely proportional to area of cross section. Therefore, the macroscopic form of ohm’s law can be stated as V = I R.
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Question 29 of 104
29. Question
Which is the ratio of potential difference across the given conductor to the current passing through the conductor?
Correct
The resistance is the ratio of potential difference across the given conductor to the current passing through the conductor. R = V / I.
Incorrect
The resistance is the ratio of potential difference across the given conductor to the current passing through the conductor. R = V / I.
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Question 30 of 104
30. Question
What is the SI unit of resistance?
Correct
The SI unit of resistance is ohm (Ω). The graph between current versus voltage is straight line with a slope equal to the inverse of resistance R of the conductor.
Incorrect
The SI unit of resistance is ohm (Ω). The graph between current versus voltage is straight line with a slope equal to the inverse of resistance R of the conductor.
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Question 31 of 104
31. Question
A potential difference across 24 Ω resistor is 12 V. What is the current through the resistor?
Correct
V = 12 V and R = 24 Ω
Current, I =?
From Ohm’s law, I = V / R = 12 / 24 = 0.5 A.
Incorrect
V = 12 V and R = 24 Ω
Current, I =?
From Ohm’s law, I = V / R = 12 / 24 = 0.5 A.
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Question 32 of 104
32. Question
An electric cell converts which energy into electrical energy to produce electricity?
Correct
An electric cell converts chemical energy into electrical energy to produce electricity. It contains two electrodes (carbon and zinc) immersed in an electrolyte (sulphuric acid).
Incorrect
An electric cell converts chemical energy into electrical energy to produce electricity. It contains two electrodes (carbon and zinc) immersed in an electrolyte (sulphuric acid).
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Question 33 of 104
33. Question
Which among the following statement is correct?
- Several electric cells connected together form a battery. When a cell or battery is connected to a circuit, electrons flow from the negative terminal to the positive terminal through the circuit.
- By using chemical reactions, a battery produces potential difference across its terminals. This potential difference provides the energy to move the electrons through the circuit. Commercially available electric cells and batteries.
Correct
Incorrect
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Question 34 of 104
34. Question
Which among the following statement is correct
- A battery or cell is called a source of electromotive force (emf). The term ‘electromotive force’ is a misnomer since it does not really refer to a force but describes a potential difference in volts. The emf of a battery or cell is the voltage provided by the battery when no current flows in the external circuit.
- Electromotive force determines the amount of work a battery or cell has to do move a certain amount of charge around the circuit. It is denoted by the symbol ε. An ideal battery has zero internal resistance and the potential difference (terminal voltage) across the battery equals to its emf.
- In reality, the battery is made of electrolyte than electrodes, there is resistance to the flow of charges within the battery. This resistance is called external resistance r. For a real battery, the terminal voltage is equal to the emf of the battery. A freshly prepared cell has low internal resistance and it increases with ageing.
Correct
In reality, the battery is made of electrodes and electrolyte, there is resistance to the flow of charges within the battery. This resistance is called internal resistance r. For a real battery, the terminal voltage is not equal to the emf of the battery. A freshly prepared cell has low internal resistance and it increases with ageing.
Incorrect
In reality, the battery is made of electrodes and electrolyte, there is resistance to the flow of charges within the battery. This resistance is called internal resistance r. For a real battery, the terminal voltage is not equal to the emf of the battery. A freshly prepared cell has low internal resistance and it increases with ageing.
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Question 35 of 104
35. Question
The emf of cell ε is measured by what?
Correct
The emf of cell ε is measured by connecting a high resistance voltmeter across it without connecting the external resistance R. Since the voltmeter draws very little current for deflection, the circuit may be considered as open. Hence the voltmeter reading gives the emf of the cell.
Incorrect
The emf of cell ε is measured by connecting a high resistance voltmeter across it without connecting the external resistance R. Since the voltmeter draws very little current for deflection, the circuit may be considered as open. Hence the voltmeter reading gives the emf of the cell.
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Question 36 of 104
36. Question
What is the SI unit of electrical resistivity?
Correct
The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section. The SI unit of ρ is ohm-metre (Ω m).
Incorrect
The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section. The SI unit of ρ is ohm-metre (Ω m).
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Question 37 of 104
37. Question
Which among the following is the semiconductor?
Correct
The germanium and silicon are semiconductor. Their resistivity, ρ (Ω m) at 200 C 0.46 and 640.
Incorrect
The germanium and silicon are semiconductor. Their resistivity, ρ (Ω m) at 200 C 0.46 and 640.
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Question 38 of 104
38. Question
Which among the following is not the conductor?
Correct
Pure water is insulator. Other insulators are glass, hard rubber, NaCl, Fused Quartz.
Incorrect
Pure water is insulator. Other insulators are glass, hard rubber, NaCl, Fused Quartz.
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Question 39 of 104
39. Question
When two or more resistors are connected end to end, they are said to be in ____
Correct
When two or more resistors are connected end to end, they are said to be in series. The resistors could be simple resistors or bulbs or heating elements or other devices.
Incorrect
When two or more resistors are connected end to end, they are said to be in series. The resistors could be simple resistors or bulbs or heating elements or other devices.
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Question 40 of 104
40. Question
Which among the following statement is correct
- Resistors are in parallel when they are connected across the same potential difference. In this case, the total current I that leaves the battery is split into three separate components. Let I1, I2 and I3 be the current through the resistors R1 , R2 and R3
- Due to the conservation of charge, total current in the circuit I is equal to sum of the currents through each of the three resistors. Since the voltage across each resistor is the same, applying Ohm’s law to each resistor, we have I1 = V/R1, I2 = V/R2, I3 = V/R Thus, we get 1/Rp = 1/R1 + 1/R2 + 1/R3.
- Here RP is the equivalent resistance of the parallel combination of the resistors. Thus, when a number of resistors are connected in parallel, the sum of the reciprocals of resistance of the individual resistors is more than the reciprocal of the effective resistance of the combination. The value of equivalent resistance in parallel connection will be grater than each individual resistance.
Correct
Here RP is the equivalent resistance of the parallel combination of the resistors. Thus, when a number of resistors are connected in parallel, the sum of the reciprocals of resistance of the individual resistors is equal to the reciprocal of the effective resistance of the combination. The value of equivalent resistance in parallel connection will be lesser than each individual resistance.
Incorrect
Here RP is the equivalent resistance of the parallel combination of the resistors. Thus, when a number of resistors are connected in parallel, the sum of the reciprocals of resistance of the individual resistors is equal to the reciprocal of the effective resistance of the combination. The value of equivalent resistance in parallel connection will be lesser than each individual resistance.
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Question 41 of 104
41. Question
Carbon resistors consists of a which core, on which a thin layer of crystalline carbon is deposited?
Correct
Carbon resistors consists of a ceramic core, on which a thin layer of crystalline carbon is deposited. These resistors are inexpensive, stable and compact in size. Colour rings are used to indicate the value of the resistance.
Incorrect
Carbon resistors consists of a ceramic core, on which a thin layer of crystalline carbon is deposited. These resistors are inexpensive, stable and compact in size. Colour rings are used to indicate the value of the resistance.
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Question 42 of 104
42. Question
In three coloured ring which ring indicates the decimal multiplier after them?
Correct
Three coloured rings are used to indicate the values of a resistor: the first two rings are significant figures of resistances; the third ring indicates the decimal multiplier after them.
Incorrect
Three coloured rings are used to indicate the values of a resistor: the first two rings are significant figures of resistances; the third ring indicates the decimal multiplier after them.
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Question 43 of 104
43. Question
What is the tolerance of carbon resistors if there is no fourth ring?
Correct
Three coloured rings are used to indicate the values of a resistor: the first two rings are significant figures of resistances, the third ring indicates the decimal multiplier after them. The fourth colour, silver or gold, shows the tolerance of the resistor at 10% or 5%. If there is no fourth ring, the tolerance is 20%.
Incorrect
Three coloured rings are used to indicate the values of a resistor: the first two rings are significant figures of resistances, the third ring indicates the decimal multiplier after them. The fourth colour, silver or gold, shows the tolerance of the resistor at 10% or 5%. If there is no fourth ring, the tolerance is 20%.
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Question 44 of 104
44. Question
Which among the following statement is correct
- The resistivity of a material is dependent on temperature. It is experimentally found that for a wide range of temperatures, the resistivity of a conductor increases with decrease in temperature according to the expression. ΡT = ρ0 [1 + α(T ̶ T0 )]
- Where ρT is the resistivity of a conductor at ToC, ρo is the resistivity of the conductor at some reference temperature To (usually at 20o C) and α is the temperature coefficient of resistivity. It is defined as the ratio of increase in resistivity per degree rise in temperature to its resistivity at To. α = ∆ρ/ ρo∆T
Correct
The resistivity of a material is dependent on temperature. It is experimentally found that for a wide range of temperatures, the resistivity of a conductor increases with increase in temperature according to the expression, ΡT = ρ0 [1 + α (T ̶ T0)].
Incorrect
The resistivity of a material is dependent on temperature. It is experimentally found that for a wide range of temperatures, the resistivity of a conductor increases with increase in temperature according to the expression, ΡT = ρ0 [1 + α (T ̶ T0)].
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Question 45 of 104
45. Question
Which among the following statement is correct?
- For conductors α is negative. If the temperature of a conductor decreases, the average kinetic energy of electrons in the conductor increases. This results in more frequent collisions and hence the resistivity decreases.
- Even though, the resistivity of conductors like metals varies linearly for wide range of temperatures, there also exists a non-linear region at very low temperatures. The resistivity approaches some finite value as the temperature approaches absolute zero.
- For semiconductors, the resistivity decreases with increase in temperature. As the temperature increases, more electrons will be liberated from their atoms. Hence the current increases and therefore the resistivity decreases
Correct
For conductors α is positive. If the temperature of a conductor increases, the average kinetic energy of electrons in the conductor increases. This results in more frequent collisions and hence the resistivity increases.
Incorrect
For conductors α is positive. If the temperature of a conductor increases, the average kinetic energy of electrons in the conductor increases. This results in more frequent collisions and hence the resistivity increases.
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Question 46 of 104
46. Question
A semiconductor with a negative temperature coefficient of resistivity is called _____
Correct
A semiconductor with a negative temperature coefficient of resistivity is called a thermistor. The electrical conductivity, σ = ne2 τ / m. As the resistivity is inverse of σ, it can be written as ρ = m / ne2τ
Incorrect
A semiconductor with a negative temperature coefficient of resistivity is called a thermistor. The electrical conductivity, σ = ne2 τ / m. As the resistivity is inverse of σ, it can be written as ρ = m / ne2τ
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Question 47 of 104
47. Question
Which among the following statement is correct
- The resistivity of materials is inversely proportional to the number density (n) of the electrons.
- The resistivity of materials is inversely proportional to the average time between the collisions (τ).
- The resistivity of materials is directly proportional to the number density (n) of the electrons.
Correct
Incorrect
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Question 48 of 104
48. Question
In which among the following, if the temperature increases, the average time between the collision (τ) decreases and n is independent of temperature?
Correct
In metals, if the temperature increases, the average time between the collision (τ) decreases and n is independent of temperature. In semiconductors when temperature increases, n increases and τ decreases, but increase in n is dominant than decreasing τ, so that overall resistivity decreases.
Incorrect
In metals, if the temperature increases, the average time between the collision (τ) decreases and n is independent of temperature. In semiconductors when temperature increases, n increases and τ decreases, but increase in n is dominant than decreasing τ, so that overall resistivity decreases.
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Question 49 of 104
49. Question
The resistance of certain materials become zero below certain temperature Tc. This temperature is known as _____
Correct
The resistance of certain materials become zero below certain temperature Tc. This temperature is known as critical temperature or transition temperature.
Incorrect
The resistance of certain materials become zero below certain temperature Tc. This temperature is known as critical temperature or transition temperature.
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Question 50 of 104
50. Question
The materials which exhibit critical temperature or transition temperature property are known as _____
Correct
The materials which exhibit critical temperature or transition temperature property are known as superconductors. This phenomenon was first observed by Kammerlingh Onnes in 1911.
Incorrect
The materials which exhibit critical temperature or transition temperature property are known as superconductors. This phenomenon was first observed by Kammerlingh Onnes in 1911.
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Question 51 of 104
51. Question
Kammerlingh Onnes found that which element exhibits superconductor behaviour at 4.2 K. Since R = 0, current once induced in a superconductor persists without any potential difference?
Correct
Kammerlingh Onnes found that mercury exhibits superconductor behaviour at 4.2 K. Since R = 0, current once induced in a superconductor persists without any potential difference.
Incorrect
Kammerlingh Onnes found that mercury exhibits superconductor behaviour at 4.2 K. Since R = 0, current once induced in a superconductor persists without any potential difference.
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Question 52 of 104
52. Question
If the resistance of coil is 3 Ω at 200 C and α = 0.004/0 C then determine its resistance at 1000 C?
Correct
R0 = 3 Ω, T = 1000 C, T0 = 200 C
α = 0.004/0 C, RT=?
RT = R0 (1 + α (T-T0))
R100 = 3(1 + 0.004 × 80)
R100 = 3.96 Ω.
Incorrect
R0 = 3 Ω, T = 1000 C, T0 = 200 C
α = 0.004/0 C, RT=?
RT = R0 (1 + α (T-T0))
R100 = 3(1 + 0.004 × 80)
R100 = 3.96 Ω.
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Question 53 of 104
53. Question
Resistance of a material at 200 C and 400 C are 45 Ω and 85 Ω respectively. Find its temperature coefficient of resistivity.
- α = 0.044 pero C
- α = 0.192 pero C
- α = 1.074 pero C
- α = 2.840 pero C
Correct
Explanation
T0 = 20 0 C, T = 40 0 C, R0 = 45 Ω, R= 85 Ω
α = = = 1/45 (2)
α = 0.044 pero C
Incorrect
Explanation
T0 = 20 0 C, T = 40 0 C, R0 = 45 Ω, R= 85 Ω
α = = = 1/45 (2)
α = 0.044 pero C
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Question 54 of 104
54. Question
Which among the following statement is correct
- When a battery is connected between the ends of a conductor, a current is established. The battery is supplying energy to the device which is connected in the circuit. Consider a circuit in which a battery of voltage V is connected to the resistor.
- Assume that a positive charge of dQ moves from point a to b through the battery and moves from point c to d through the resistor and back to point a. When the charge moves from point a to b, it gains potential energy dU = V.dQ and the chemical potential energy of the battery decreases by the same amount.
- When this charge dQ passes through resistor it loses the potential energy dU = V.dQ due to collision with atoms in the resistor and again reaches the point a. This process occurs continuously till the battery is connected in the circuit. The rate at which the charge loses its electrical potential energy in the resistor can be calculated.
Correct
Incorrect
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Question 55 of 104
55. Question
The electrical power produced (dissipated) by a resistor is ____
Correct
The electrical power produced (dissipated) by a resistor is I2 R. It depends on the square of the current. Hence, if current is doubled, the power will increase by four times. Similar explanation holds true for voltage also.
Incorrect
The electrical power produced (dissipated) by a resistor is I2 R. It depends on the square of the current. Hence, if current is doubled, the power will increase by four times. Similar explanation holds true for voltage also.
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Question 56 of 104
56. Question
Using which law power delivered to the resistance R is expressed in other forms like P = IV = I (IR) = I2 R?
Correct
Using Ohm’s law, power delivered to the resistance R is expressed in other forms P = IV = I (IR) = I 2 R and P = IV = (V/R) V = V2 / R.
Incorrect
Using Ohm’s law, power delivered to the resistance R is expressed in other forms P = IV = I (IR) = I 2 R and P = IV = (V/R) V = V2 / R.
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Question 57 of 104
57. Question
If the power is in watts and the time is in seconds, the energy will be in ____
Correct
The total electrical energy used by any device is obtained by multiplying the power and duration of the time when it is ON. If the power is in watts and the time is in seconds, the energy will be in joules.
Incorrect
The total electrical energy used by any device is obtained by multiplying the power and duration of the time when it is ON. If the power is in watts and the time is in seconds, the energy will be in joules.
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Question 58 of 104
58. Question
In practice, electrical energy is measured in ____
Correct
In practice, electrical energy is measured in kilowatt hour (kWh). 1 kWh is known as 1 unit of electrical energy. (1 kWh = 1000 Wh = (1000 W) (3600 s) = 3.6 × 106 J)
Incorrect
In practice, electrical energy is measured in kilowatt hour (kWh). 1 kWh is known as 1 unit of electrical energy. (1 kWh = 1000 Wh = (1000 W) (3600 s) = 3.6 × 106 J)
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Question 59 of 104
59. Question
Which among the following statement is correct
- The Tamil Nadu Electricity Board is charging for the amount of energy you use and not for the power. A current of 1A flowing through a potential difference of 1V produces a power of 1W.
- The Tamil Nadu Electricity Board is charging for the amount of power you use and not for the energy. A current of 1A flowing through a potential difference of 1V produces a power of 0.5W
Correct
Incorrect
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Question 60 of 104
60. Question
When current flows through a resistor, some of the electrical energy delivered to the resistor is converted into heat energy and it is dissipated. This heating effect of current is known as ____
Correct
When current flows through a resistor, some of the electrical energy delivered to the resistor is converted into heat energy and it is dissipated. This heating effect of current is known as Joule’s heating effect.
Incorrect
When current flows through a resistor, some of the electrical energy delivered to the resistor is converted into heat energy and it is dissipated. This heating effect of current is known as Joule’s heating effect.
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Question 61 of 104
61. Question
Which among the following statement is correct
- Due to internal resistance r of the cell, the voltmeter reads a value V, which is less than the emf of cell ε. It is because, certain amount of voltage (Ir) has dropped across the internal resistance r. Then V = ε – Ir. , Ir = ε – V
- Dividing V = IR in Ir = ε – V, we get r = [(ε – V)/V] R. Since ε, V and R are known, internal resistance r can be determined. We can also find the total current that flows in the circuit. Due to this internal resistance, the power delivered to the circuit is not equal to power rating mentioned in the battery.
- For a battery of emf ε, with an internal resistance r, the power delivered to the circuit of resistance R is given by P = Iε = I (V + Ir). Here V is the voltage drop across the resistance R and it is equal to IR. Therefore, P = I (IR +Ir) i.e., P = I2 R + I2
Correct
Incorrect
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Question 62 of 104
62. Question
Which among the following statement is correct
- In P = I2 R + I2 r, I2r is the power delivered to the internal resistance and I 2 R is the power delivered to the electrical device (here it is the resistance R).
- For a good battery, the internal resistance r is very small, then I 2 R << I 2 r and almost entire power is delivered to the external resistance.
Correct
For a good battery, the internal resistance r is very small, then I 2 r << I 2 R and almost entire power is delivered to the external resistance.
Incorrect
For a good battery, the internal resistance r is very small, then I 2 r << I 2 R and almost entire power is delivered to the external resistance.
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Question 63 of 104
63. Question
A battery has an emf of 12 V and connected to a resistor of 3 Ω. The current in the circuit is 3.93A. Calculate (a) terminal voltage and the internal resistance of the battery.
Correct
The terminal voltage of the battery is equal to voltage drop across the resistor
V = IR = 3.93 × 3 = 11.79 V
The internal resistance of the battery,
r = [(ε – V)/V] R = [(12 – 11.79) / 11.79] 3
= 0.05 Ω.
Incorrect
The terminal voltage of the battery is equal to voltage drop across the resistor
V = IR = 3.93 × 3 = 11.79 V
The internal resistance of the battery,
r = [(ε – V)/V] R = [(12 – 11.79) / 11.79] 3
= 0.05 Ω.
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Question 64 of 104
64. Question
Which among the following statement is correct
- Several cells can be connected to form a battery. In series connection, the negative terminal of one cell is connected to the positive terminal of the second cell, the negative terminal of second cell is connected to the positive terminal of the third cell and so on. The free positive terminal of the first cell and the free negative terminal of the last cell become the terminals of the battery.
- Suppose n cells, each of emf ε volts and internal resistance r ohms are connected in series with an external resistance R. By Ohm’s law, the current in the circuit is I = total emf / total resistance = n ε / (nr + R). In case a, If r << R, then I = (n ε / R) ≈ nI1. Where, I1 is the current due to a single cell I1 = ε/R. Thus, if r is negligible when compared to R the current supplied by the battery is n times that supplied by a single cell.
- In case of b If r>>R, I = (n ε/n r) ≈ ε / r. It is the current due to a multiple cell. That is, current due to the whole battery is larger than that due to a single cell and hence there is more advantage in connecting several cells. Thus, series connection of cells is advantageous only when the effective internal resistance of the cells is negligibly small compared with R.
Correct
In case of b If r>>R, I = (n ε/n r) ≈ ε / r. It is the current due to a single cell. That is, current due to the whole battery is the same as that due to a single cell and hence there is no advantage in connecting several cells. Thus, series connection of cells is advantageous only when the effective internal resistance of the cells is negligibly small compared with R.
Incorrect
In case of b If r>>R, I = (n ε/n r) ≈ ε / r. It is the current due to a single cell. That is, current due to the whole battery is the same as that due to a single cell and hence there is no advantage in connecting several cells. Thus, series connection of cells is advantageous only when the effective internal resistance of the cells is negligibly small compared with R.
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Question 65 of 104
65. Question
A battery has an emf of 12 V and connected to a resistor of 3 Ω. The current in the circuit is 3.93A. Calculate power delivered by the battery and power delivered to the resistor
Correct
The power delivered by the battery P = Iε = 3.93 × 12 = 47.1 W
The power delivered to the resistor = I2 R = 46.3 W
The remaining power P = (47.1 – 46.3) = 0.8 W is delivered to the internal resistance and cannot be used to do useful work. (It is equal to I 2 r).
Incorrect
The power delivered by the battery P = Iε = 3.93 × 12 = 47.1 W
The power delivered to the resistor = I2 R = 46.3 W
The remaining power P = (47.1 – 46.3) = 0.8 W is delivered to the internal resistance and cannot be used to do useful work. (It is equal to I 2 r).
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Question 66 of 104
66. Question
Which among the following statement is correct
- In parallel connection all the positive terminals of the cells are connected to one point and all the negative terminals to a second point. These two points form the positive and negative terminals of the battery. Let n cells be connected in parallel between the points A and B and a resistance R is connected between the points A and B. Let ε be the emf and r the internal resistance of each cell.
- The total emf is the potential difference between the points A and B, which is equal to ε. The current in the circuit is given by I = [ε / ((r/n) + R)]. Thus, I = n ε/ (r + n R). In case of a If r >> R, I = (n ε/ r) = n I1. Where I1 is the current due to a single cell (ε/r) when R is negligible. Thus, the current through the external resistance due to the whole battery is n times the current due to a single cell.
- In case of b, If r<< R, I = ε / R. The above equation implies that current due to the whole battery is the same as that due to a single cell. Hence it is advantageous to connect cells in parallel when the external resistance is very small compared to the internal resistance of the cells.
Correct
Incorrect
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Question 67 of 104
67. Question
When the car engine is started with headlights turned on, they sometimes become dim. This is due to ____
Correct
When the car engine is started with headlights turned on, they sometimes become dim. This is due to the internal resistance of the car battery.
Incorrect
When the car engine is started with headlights turned on, they sometimes become dim. This is due to the internal resistance of the car battery.
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Question 68 of 104
68. Question
Which among the following is used to find current and voltage in complex circuit?
Correct
Ohm’s law is useful only for simple circuits. For more complex circuits, Kirchhoff ’s rules can be used to find current and voltage. There are two generalized rules: i) Kirchhoff ’s current rule ii) Kirchhoff ’s voltage rule. Ohm’s law is useful only for simple circuits. For more complex circuits, Kirchhoff ’s rules can be used to find current and voltage. There are two generalized rules: i) Kirchhoff ’s current rule ii) Kirchhoff ’s voltage rule.
Incorrect
Ohm’s law is useful only for simple circuits. For more complex circuits, Kirchhoff ’s rules can be used to find current and voltage. There are two generalized rules: i) Kirchhoff ’s current rule ii) Kirchhoff ’s voltage rule. Ohm’s law is useful only for simple circuits. For more complex circuits, Kirchhoff ’s rules can be used to find current and voltage. There are two generalized rules: i) Kirchhoff ’s current rule ii) Kirchhoff ’s voltage rule.
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Question 69 of 104
69. Question
Which among the following is not the other name of Kirchhoff’s first rule?
Correct
The other name of Kirchhoff’s first rule are Current rule or Junction rule.
Incorrect
The other name of Kirchhoff’s first rule are Current rule or Junction rule.
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Question 70 of 104
70. Question
Which among the following is the other name of Kirchhoff’s Second rule?
Correct
The other name of Kirchhoff’s Second rule is Voltage rule or Loop rule.
Incorrect
The other name of Kirchhoff’s Second rule is Voltage rule or Loop rule.
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Question 71 of 104
71. Question
Which among the following statement is correct
- Kirchhoff’s first rule states that the algebraic sum of the currents at any junction of a circuit is zero. It is a statement of law of conservation of electric charge. The charges that enter a given junction in a circuit must leave that junction since charge cannot build up or disappear at a junction. By convention, current entering the junction is taken as positive and current leaving the junction is taken as negative.
- Kirchhoff’s Second rule states that in a open circuit the algebraic sum of the products of the current and resistance of each part of the circuit is equal to the total emf included in the circuit. This rule follows from the law of conservation of mass for an isolated system (The energy supplied by the emf sources is equal to the sum of the energy delivered to all resistors).
- The product of current and resistance is taken as positive when the direction of the current is followed. Suppose if the direction of current is opposite to the direction of the loop, then product of current and voltage across the resistor is negative. The emf is considered positive when proceeding from the negative to the positive terminal of the cell. Kirchhoff voltage rule has to be applied only when all currents in the circuit reach a steady state condition (the current in various branches are constant).
Correct
Kirchhoff’s Second rule states that in a closed circuit the algebraic sum of the products of the current and resistance of each part of the circuit is equal to the total emf included in the circuit. This rule follows from the law of conservation of energy for an isolated system (The energy supplied by the emf sources is equal to the sum of the energy delivered to all resistors).
Incorrect
Kirchhoff’s Second rule states that in a closed circuit the algebraic sum of the products of the current and resistance of each part of the circuit is equal to the total emf included in the circuit. This rule follows from the law of conservation of energy for an isolated system (The energy supplied by the emf sources is equal to the sum of the energy delivered to all resistors).
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Question 72 of 104
72. Question
Which is an instrument used for detecting and measuring even very small electric currents and is extensively useful to compare the potential difference between various parts of the circuit?
Correct
A galvanometer is an instrument used for detecting and measuring even very small electric currents. It is extensively useful to compare the potential difference between various parts of the circuit.
Incorrect
A galvanometer is an instrument used for detecting and measuring even very small electric currents. It is extensively useful to compare the potential difference between various parts of the circuit.
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Question 73 of 104
73. Question
Which among the following statement is correct regarding Wheatstone’s bridge?
- An important application of Kirchhoff ’s rules is the Wheatstone’s bridge. It is used to compare resistances and in determining the unknown resistance in electrical network. The bridge consists of four resistances P, Q, R and S connected. A galvanometer G is connected between the points B and D. The battery is connected between the points A and C.
- The current through the galvanometer is IG and its resistance is G. Applying Kirchhoff ’s current rule to junction B and D respectively. We get 1. I1 – IG – I3 = 0 and 2. I2 + IG – I4 = 0. Applying Kirchhoff ’s voltage rule to loop ABDA, we get 3. I1 P + IGG – I2 R = 0. Applying Kirchhoff ’s voltage rule to loop ABCDA, 4. I1 P + I3 Q – I4 S – I2 R = 0. When the points B and D are at the same potential, the bridge is said to be balanced.
- As there is no potential difference between B and D, no current flows through galvanometer (IG = 0). Substituting IG = 0 in equation 1, 2 and 3, we get A. I1 = I3, B. I2 = I4, and C. I1P = I2 using C in 4 we get D. I3 Q = I4 S. Dividing equation D by equation C, we get P/Q = R/S. This is the condition for bridge balance. Only under this condition, galvanometer shows null deflection. Suppose we know the values of two adjacent resistances, the other two resistances can be compared.
Correct
Incorrect
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Question 74 of 104
74. Question
What is the value of x when the Wheatstone’s network is balanced?
P = 500 Ω, Q = 800 Ω, R = x + 400, S = 1000 Ω
Correct
P/Q = R/S, when the network is balanced
500/800 = (x+4000)/1000
x + 400 = (5/8) + 1000
x + 400 = 625
x = 625 – 400
x = 225 Ω.
Incorrect
P/Q = R/S, when the network is balanced
500/800 = (x+4000)/1000
x + 400 = (5/8) + 1000
x + 400 = 625
x = 625 – 400
x = 225 Ω.
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Question 75 of 104
75. Question
Which among the following statement is correct regarding meter bridge?
- The meter bridge is not another form of Wheatstone’s bridge. It consists of a non-uniform wire of manganin AB of one meter length. This wire is stretched along a metre scale on a wooden board between two copper strips C and D. Between these two copper strips another copper strip E is mounted to enclose two gaps G1 and G2.
- An unknown resistance P is connected in G1 and a standard resistance Q is connected in G2. A jockey (conducting wire-contact maker) is connected to the terminal E on the central copper strip through a galvanometer (G) and a high resistance (HR). The exact position of jockey on the wire can be read on the scale. A Lechlanche cell and a key (K) are connected between the ends of the bridge wire.
- The position of the jockey on the wire is adjusted so that the galvanometer shows zero deflection. Let the position of jockey at the wire be at J. The resistances corresponding to AJ and JB of the bridge wire form the resistances R and S of the Wheatstone’s bridge. Then for the bridge balance = = . where r is the resistance per unit length of wire. = .
Correct
The meter bridge is another form of Wheatstone’s bridge. It consists of a uniform wire of manganin AB of one meter length. This wire is stretched along a metre scale on a wooden board between two copper strips C and D. Between these two copper strips another copper strip E is mounted to enclose two gaps G1 and G2.
Incorrect
The meter bridge is another form of Wheatstone’s bridge. It consists of a uniform wire of manganin AB of one meter length. This wire is stretched along a metre scale on a wooden board between two copper strips C and D. Between these two copper strips another copper strip E is mounted to enclose two gaps G1 and G2.
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Question 76 of 104
76. Question
In a meter bridge experiment with a standard resistance of 15 Ω in the right gap, the ratio of balancing length is 3:2. Find the value of the other resistance?
Correct
Q = 15 Ω, l1 : l2 = 3:2
l1/ l2 = 3 / 2
P / Q = l1 / l2
P = Q (l1 / l2)
P = 15 × (3 / 2) = 22.5 Ω.
Incorrect
Q = 15 Ω, l1 : l2 = 3:2
l1/ l2 = 3 / 2
P / Q = l1 / l2
P = Q (l1 / l2)
P = 15 × (3 / 2) = 22.5 Ω.
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Question 77 of 104
77. Question
Which among the following statement is correct regarding potentiometer
- Potentiometer is used for the accurate measurement of potential differences, current and resistances. It consists of one-meter-long uniform wire of manganin or constantan stretched in parallel rows each of 0.1-meter length, on a wooden board. The two free ends A and B are brought to the same side and fixed to silver strips with binding screws. A meter scale is fixed series to the wire. A jockey is provided for making contact.
- A steady current is maintained across the wire CD by a battery Bt. The battery, key and the potentiometer wire connected in series form the primary circuit. The positive terminal of a primary cell of emf ε is connected to the point C and negative terminal is connected to the jockey through a galvanometer G and a high resistance HR. This forms the secondary circuit.
- Let the contact be made at any point J on the wire by jockey. If the potential difference across CJ is equal to the emf of the cell ε, then no current will flow through the galvanometer and it will show zero deflection. CJ is the balancing length l. The potential difference across CJ is equal to Irl where I is the current flowing through the wire and r is the resistance per unit length of the wire. Hence ε = Irl.
Correct
Potentiometer is used for the accurate measurement of potential differences, current and resistances. It consists of ten-meter-long uniform wire of manganin or constantan stretched in parallel rows each of 1 meter length, on a wooden board. The two free ends A and B are brought to the same side and fixed to copper strips with binding screws. A meter scale is fixed parallel to the wire. A jockey is provided for making contact.
Incorrect
Potentiometer is used for the accurate measurement of potential differences, current and resistances. It consists of ten-meter-long uniform wire of manganin or constantan stretched in parallel rows each of 1 meter length, on a wooden board. The two free ends A and B are brought to the same side and fixed to copper strips with binding screws. A meter scale is fixed parallel to the wire. A jockey is provided for making contact.
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Question 78 of 104
78. Question
In a meter bridge experiment, the value of resistance in the resistance box connected in the right gap is 10 Ω. The balancing length is l1 = 55 cm. Find the value of unknown resistance?
Correct
Q = 10 Ω
= =
P = Q × =
P = 550 / 45
P = 12.2 Ω.
Incorrect
Q = 10 Ω
= =
P = Q × =
P = 550 / 45
P = 12.2 Ω.
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Question 79 of 104
79. Question
Which among the following statement is correct regarding Comparison of emf of two cells with a potentiometer
- To compare the emf of two cells, the circuit connections are made. Potentiometer wire CD is connected to a battery Bt and a key K in series. This is the primary circuit. The end C of the wire is connected to the terminal M of a DPDT (Double Pole Double Throw) switch and the other terminal N is connected to a jockey through a galvanometer G and a high resistance HR.
- The cells whose emf ε1 and ε2 to be compared are connected to the terminals M1, N1 and M2, N2 of the DPDT switch. The positive terminals of Bt, ε1 and ε2 should be connected to the same end C. The DPDT switch is pressed towards M1, N1 so that cell ε1 is included in the secondary circuit and the balancing length l1 is found by adjusting the jockey for zero deflection.
- Then the second cell ε2 is included in the circuit and the balancing length l2 is determined. Let r be the resistance per unit length of the potentiometer wire and I be the current flowing through the wire. we have ε1 = Irl1 and ε2 = Irl2. By dividing ε1 and ε2, we get (ε1 / ε2) = (l1 / l2). By including a rheostat (Rh) in the primary circuit, the experiment can be repeated several times by changing the current flowing through it.
Correct
Incorrect
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Question 80 of 104
80. Question
Which among the following statement is correct regarding measurement of internal resistance of a cell by potentiometer?
Correct
A suitable resistance (say, 10 Ω) is included in the resistance box and key K2 is closed. Let r be the internal resistance of the cell. The current passing through the cell and the resistance R is given by I = . The potential difference across R is V = . When this potential difference is balanced on the potentiometer wire, let l2 be the balancing length. Then ∝ l2 (B). From equation A and B, we get r = R ().
Incorrect
A suitable resistance (say, 10 Ω) is included in the resistance box and key K2 is closed. Let r be the internal resistance of the cell. The current passing through the cell and the resistance R is given by I = . The potential difference across R is V = . When this potential difference is balanced on the potentiometer wire, let l2 be the balancing length. Then ∝ l2 (B). From equation A and B, we get r = R ().
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Question 81 of 104
81. Question
As current produces thermal energy, thermal energy may also be suitably used to produce an electromotive force. This is known as ______
Correct
As current produces thermal energy, thermal energy may also be suitably used to produce an electromotive force. This is known as thermoelectric effect.
Incorrect
As current produces thermal energy, thermal energy may also be suitably used to produce an electromotive force. This is known as thermoelectric effect.
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Question 82 of 104
82. Question
Which among the following statement is correct
- If a current I flow through a conductor kept across a potential difference V for a time t, the work done or the electric potential energy spent is W = VIt.
- In the absence of any other external effect, this energy is spent in heating the conductor. The amount of heat(H) produced is H = VIt. For a resistance R, H = I2 This relation was experimentally verified by newton and is known as newton’s law of heating.
- It states that the heat developed in an electrical circuit due to the flow of current varies directly as (i) the square of the current (ii) the resistance of the circuit and (iii) the time of flow.
Correct
In the absence of any other external effect, this energy is spent in heating the conductor. The amount of heat(H) produced is H = Vit. For a resistance R, H = I2 Rt. This relation was experimentally verified by Joule and is known as Joule’s law of heating.
Incorrect
In the absence of any other external effect, this energy is spent in heating the conductor. The amount of heat(H) produced is H = Vit. For a resistance R, H = I2 Rt. This relation was experimentally verified by Joule and is known as Joule’s law of heating.
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Question 83 of 104
83. Question
Find the heat energy produced in a resistance of 10 Ω when 5 A current flows through it for 5 minutes?
Correct
R = 10 Ω, I = 5 A, t = 5 minutes = 5 × 60 s
H = I2 R t = 52 × 10 × 5 × 60 = 25 × 10 × 300
= 25 × 3000
= 75000 J (or) 75 kJ.
Incorrect
R = 10 Ω, I = 5 A, t = 5 minutes = 5 × 60 s
H = I2 R t = 52 × 10 × 5 × 60 = 25 × 10 × 300
= 25 × 3000
= 75000 J (or) 75 kJ.
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Question 84 of 104
84. Question
In Electric heaters, the heating elements are not made of which among the following metal?
Correct
Electric iron, electric heater, electric toaster are some of the home appliances that utilize the heating effect of current. In these appliances, the heating elements are made of nichrome, an alloy of nickel and chromium.
Incorrect
Electric iron, electric heater, electric toaster are some of the home appliances that utilize the heating effect of current. In these appliances, the heating elements are made of nichrome, an alloy of nickel and chromium.
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Question 85 of 104
85. Question
Which among the following metal has a high specific resistance and can be heated to very high temperatures without oxidation?
Correct
Nichrome has a high specific resistance and can be heated to very high temperatures without oxidation.
Incorrect
Nichrome has a high specific resistance and can be heated to very high temperatures without oxidation.
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Question 86 of 104
86. Question
Which are connected in series in a circuit to protect the electric devices from the heat developed by the passage of excessive current?
Correct
Fuses as shown in Figure 2.31, are connected in series in a circuit to protect the electric devices from the heat developed by the passage of excessive current. It is a short length of a wire made of a low melting point material. It melts and breaks the circuit if current exceeds a certain value.
Incorrect
Fuses as shown in Figure 2.31, are connected in series in a circuit to protect the electric devices from the heat developed by the passage of excessive current. It is a short length of a wire made of a low melting point material. It melts and breaks the circuit if current exceeds a certain value.
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Question 87 of 104
87. Question
Which alloy is used for fuses when current rating is below 15 A?
Correct
An alloy of lead – tin is used for fuses when current rating is below 15 A.
Incorrect
An alloy of lead – tin is used for fuses when current rating is below 15 A.
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Question 88 of 104
88. Question
when current rating is above 15 A, which fuse wires are used?
Correct
When current rating is above 15 A, copper fuse wires are used. The only disadvantage with the above fuses is that once fuse wire is burnt due to excessive current, they need to be replaced.
Incorrect
When current rating is above 15 A, copper fuse wires are used. The only disadvantage with the above fuses is that once fuse wire is burnt due to excessive current, they need to be replaced.
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Question 89 of 104
89. Question
Nowadays which was used in house instead of fuses?
Correct
Nowadays in houses, circuit breakers (trippers) are also used instead of fuses. Whenever there is an excessive current produced due to faulty wire connection, the circuit breaker switch opens. After repairing the faulty connection, we can close the circuit breaker switch.
Incorrect
Nowadays in houses, circuit breakers (trippers) are also used instead of fuses. Whenever there is an excessive current produced due to faulty wire connection, the circuit breaker switch opens. After repairing the faulty connection, we can close the circuit breaker switch.
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Question 90 of 104
90. Question
Which are used to manufacture a large number of technologically important materials such as steel, silicon carbide, quartz, gallium arsenide, etc.?
Correct
Furnaces as shown in Figure 2.33 are used to manufacture a large number of technologically important materials such as steel, silicon carbide, quartz, gallium arsenide, etc.
Incorrect
Furnaces as shown in Figure 2.33 are used to manufacture a large number of technologically important materials such as steel, silicon carbide, quartz, gallium arsenide, etc.
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Question 91 of 104
91. Question
Which furnaces produce temperatures up to 3000°C?
Correct
To produce temperatures up to 1500°C, molybdenum-nichrome wire wound on a silica tube is used. Carbon arc furnaces produce temperatures up to 3000°C.
Incorrect
To produce temperatures up to 1500°C, molybdenum-nichrome wire wound on a silica tube is used. Carbon arc furnaces produce temperatures up to 3000°C.
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Question 92 of 104
92. Question
Electric lamp consists of which filament kept inside a glass bulb and heated to incandescence by current?
Correct
Electric lamp consists of a tungsten filament (melting point 33800 C) kept inside a glass bulb and heated to incandescence by current.
Incorrect
Electric lamp consists of a tungsten filament (melting point 33800 C) kept inside a glass bulb and heated to incandescence by current.
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Question 93 of 104
93. Question
In incandescent electric lamps how many percentages of electrical energy is converted into light and the rest is wasted as heat?
Correct
In incandescent electric lamps only about 5% of electrical energy is converted into light and the rest is wasted as heat. Electric discharge lamps, electric welding and electric arc also utilize the heating effect of current.
Incorrect
In incandescent electric lamps only about 5% of electrical energy is converted into light and the rest is wasted as heat. Electric discharge lamps, electric welding and electric arc also utilize the heating effect of current.
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Question 94 of 104
94. Question
Conversion of temperature differences into electrical voltage and vice versa is known as ____
Correct
Conversion of temperature differences into electrical voltage and vice versa is known as thermoelectric effect. A thermoelectric device generates voltage when there is a temperature difference on each side. If a voltage is applied, it generates a temperature difference.
Incorrect
Conversion of temperature differences into electrical voltage and vice versa is known as thermoelectric effect. A thermoelectric device generates voltage when there is a temperature difference on each side. If a voltage is applied, it generates a temperature difference.
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Question 95 of 104
95. Question
Who discovered that in a closed circuit consisting of two dissimilar metals, when the junctions are maintained at different temperatures an emf (potential difference) is developed?
Correct
Seebeck discovered that in a closed circuit consisting of two dissimilar metals, when the junctions are maintained at different temperatures an emf (potential difference) is developed.
Incorrect
Seebeck discovered that in a closed circuit consisting of two dissimilar metals, when the junctions are maintained at different temperatures an emf (potential difference) is developed.
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Question 96 of 104
96. Question
Who showed that if two points in a conductor are at different temperatures, the density of electrons at these points will differ and as a result the potential difference is created between these points?
Correct
Thomson showed that if two points in a conductor are at different temperatures, the density of electrons at these points will differ and as a result the potential difference is created between these points. Thomson effect is also reversible.
Incorrect
Thomson showed that if two points in a conductor are at different temperatures, the density of electrons at these points will differ and as a result the potential difference is created between these points. Thomson effect is also reversible.
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Question 97 of 104
97. Question
In seebeck effect, current that flows due to the emf developed is called ____
Correct
In Seebeck effect, current that flows due to the emf developed is called thermoelectric current.
Incorrect
In Seebeck effect, current that flows due to the emf developed is called thermoelectric current.
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Question 98 of 104
98. Question
In seebeck effect, the two dissimilar metals connected to form two junctions is known as ___
Correct
In seebeck effect, two dissimilar metals connected to form two junctions is known as thermocouple. If the hot and cold junctions are interchanged, the direction of current also reverses. Hence the effect is reversible. The magnitude of the emf developed in a thermocouple depends on (i) the nature of the metals forming the couple and (ii) the temperature difference between the junctions.
Incorrect
In seebeck effect, two dissimilar metals connected to form two junctions is known as thermocouple. If the hot and cold junctions are interchanged, the direction of current also reverses. Hence the effect is reversible. The magnitude of the emf developed in a thermocouple depends on (i) the nature of the metals forming the couple and (ii) the temperature difference between the junctions.
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Question 99 of 104
99. Question
Which among the following statement regarding application of seebeck effect is correct
- Seebeck effect is used in thermoelectric generators (Seebeck generators). These, thermoelectric generators are used in power plants to convert waste heat into electricity.
- This effect is utilized in automobiles as automotive thermoelectric generators for increasing fuel efficiency.
- Seebeck effect is used in thermocouples and thermopiles to measure the temperature difference between the two objects.
Correct
Incorrect
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Question 100 of 104
100. Question
When an electric current is passed through a circuit of a thermocouple, heat is evolved at one junction and absorbed at the other junction. This is known as ____
Correct
In 1834, Peltier discovered that when an electric current is passed through a circuit of a thermocouple, heat is evolved at one junction and absorbed at the other junction. This is known as Peltier effect.
Incorrect
In 1834, Peltier discovered that when an electric current is passed through a circuit of a thermocouple, heat is evolved at one junction and absorbed at the other junction. This is known as Peltier effect.
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Question 101 of 104
101. Question
Which among the following statement is correct regarding Peltier effect: Cu – Fe thermocouple?
- In the Cu-Fe thermocouple the junctions A and B are maintained at the same temperature. Let a current from a battery flow through the thermocouple. At the junction A, where the current flows from Cu to Fe, heat is absorbed and the junction A becomes cold.
- At the junction B, where the current flows from Fe to Cu heat is liberated and it becomes hot. When the direction of current is reversed, junction A gets cooled and junction B gets heated. Hence Peltier effect is irreversible.
Correct
At the junction B, where the current flows from Fe to Cu heat is liberated and it becomes hot. When the direction of current is reversed, junction A gets heated and junction B gets cooled. Hence Peltier effect is reversible.
Incorrect
At the junction B, where the current flows from Fe to Cu heat is liberated and it becomes hot. When the direction of current is reversed, junction A gets heated and junction B gets cooled. Hence Peltier effect is reversible.
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Question 102 of 104
102. Question
Which among the following statement is correct regarding Thomson effect?
- If current is passed through a copper bar AB which is heated at the middle point C, the point C will be at higher potential. This indicates that the heat is absorbed along AC and evolved along CB of the conductor. Thus, heat is transferred due to the current flow in the direction of the current. It is called positive Thomson effect.
- When the copper bar is replaced by an iron bar, heat is evolved along CA and absorbed along BC. Thus, heat is transferred due to the current flow in the direction opposite to the direction of current. It is called negative Thomson effect.
Correct
Incorrect
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Question 103 of 104
103. Question
In which among the following metal positive Thomson effect is not observed?
Correct
positive Thomson effect are observed in metal like silver, zinc, and copper
Incorrect
positive Thomson effect are observed in metal like silver, zinc, and copper
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Question 104 of 104
104. Question
In which among the following metal negative Thomson effect is not observed?
Correct
Negative Thomson effect are observed in metal like platinum, nickel, cobalt, and mercury. Cadmium metal is used in Positive Thomson effect.
Incorrect
Negative Thomson effect are observed in metal like platinum, nickel, cobalt, and mercury. Cadmium metal is used in Positive Thomson effect.
Leaderboard: Current Electricity Online Test 12th Science
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