Electricity Book Back Questions 7th Science Lesson 9
7th Science Lesson 9
9] Electricity
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
Conventional current is in the direction opposite to electron flow.
The potential difference between any two points in the circuit is the amount of energy needed to move one unit of electric charge from one point to the other.
1 milli ampere (mA) = 10-3 ampere = 1/1000 ampere
1 microampere (µA) = 10-6 ampere = 1/1000000 ampere
The electric current flow from the higher potential level to the flower potential level is just like the water flow.
An electric cell is something that provides electricity to different devices that are not fed directly or easily by the supply of electricity.
The dry cell is not really dry in nature but the quantity of water in it is very small, as the electrolyte is in the form of a paste. In other cells, the electrolyte is usually a solution.
Electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity.
All muscles of our bodies move in response to electrical impulses generated naturally in our bodies.
Short circuit: You might have observed the spark in the electric pole located nearby your house. Do you know the cause of this electric spark? This is due to the short circuiting of electricity along its path. A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit. Arc welding is a common example of the practical application of the heating due to a short circuit.
This is the material used in SIM cards, Computers and ATM cards. Do you know by which material I am mad up off? The chip which is used in SIM cards, Computers and ATM cards are made up of semiconductors namely, silicon and germanium because of their electrical conductivity lies between a conductor and an insulator.
Wires made of copper, an electrical conductor, have very low resistance. Copper wires are used to carry current in households. These wires are in turn enclosed in electrical insulators, or materials of high electrical resistance. These materials are usually made of flexible plastic.
Generation of heat due to electric current is known as the heating effect of electricity.
Choose the best answers:
1. In the circuit diagram below, 10 units of electric charge move past point x every second. What is the current in the circuit?
(a) 10 A
(b) 1 A
(c) 10 V
(d) 1 V
2. In the circuit shown, which switches (L, M or N) must be closed to light up the bulb?
(a) Switch L only
(b) Switch M only
(c) Switch M and L only
(d) Either switch L or switches M and N
3. Small amounts of electrical current are measured in milli-ampere (mA). How many milli-ampere are there in 0.25 A?
(a) 2.5 mA
(b) 25 mA
(c) 250 mA
(d) 2500 mA
4. In which of the following circuits are the bulb connected in series?
Fill in the blanks:
1. The direction of conventional current is ______________ to electron flow.
2. One unit of coulomb is charge of approximately _______________ protons or electrons.
3. __________________ is used to measure the electric current.
4. In conducting materials electrons are _______________ bounded with atoms.
5. S.I. unit of Electrical conductivity of a conductor is ______________
State true or false. If false, correct the statement:
1. Electron flow in the same direction to conventional current flow.
2. The fuse wire does not melt whenever there is overload in the wiring.
3. In a parallel circuit, the electric components are divided into branches.
4. The representation of the electric current is A.
5. The electrical conductivity of the semiconductor is in between a conductor and an insulator.
Match the following:
1. Cell – used to open or close a circuit
2. Switch – safety devices used in electric circuit
3. Circuit – a complete path for the flow of an electric current
4. Miniature circuit breaker – reset by hand, circuit becomes complete once again
5. Fuse – a device which converts chemical energy into electrical energy
Complete the analogy:
1. Water: pipe :: Electric current: ________________
2. Copper: conductor :: Wood: _______________
3. Length: metre scale :: Current: _______________
4. Milli ampere: micro ampere :: 10-3 A: ____________
Consider the statements given below and choose the correct option:
1. Assertion (A) : Copper is used to make electric wires.
Reason (R) : Copper has very low electrical resistance.
(a) Both A and R is true and R is the correct explanation of A
(b) Both A and R are true but R is N not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
(e) Both A and R is false
2. Assertion (A) : Insulators do not allow the flow of current through themselves.
Reason (R) : They have no free charge carriers.
(a) If both A and R are true and R is the correct explanation of A
(b) If both A and R are true but R is N not the correct explanation of A
(c) If A is true but R is false
(d) If both A and R are false
Answers:
Choose the correct answers:
1. 10A 2. Either switch L or switches M and N 3. 250mA 4. Circuit D
Fill in the blanks:
1. Opposite 2. 6.242x 1018 3. Ammeter 4. Loosely 5. Siemens/metre(S/m)
State True or False:
1. False
Correct Statement: Electron flow is in the opposite direction to the conventional current flow.
2. False
Correct Statement: The fuse wire melts whenever there is overload in the wiring.
3. True
4. False
Correct Statement: The representation of the electric current is I.
5. True
Match the following:
1. A device which converts chemical energy into electrical energy
2. Used to open or close a circuit
3. A complete path for the flow of an electric current
4. Reset by hand, circuit becomes complete once again
5. Safety devices used in electric circuit
Complete the analogy:
1. Wire 2. Insulator 3. Ammeter 4. 10-6A
Consider the statements given below and choose the correct option:
1.Both A and R is true and R is the correct explanation of A
2.Both A and R is true and R is the correct explanation of A