Electric Charge And Electric Current Book Back Questions 9th Science Lesson 4

9th Science Lesson 4

4] Electric Charge And Electric Current

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

Problem 1: How many electrons will be there in one coulomb of charge?

Solution: Charge on 1 electron, e = 1.6 x 10^-19 C q = ne or n = q/e

⸫ Number of electrons in 1 coulomb = 1/1.6 x 10^-19 = 6.25 x 10¹⁸ electrons.

Electrostatic forces between two point charges obey Newton’s third law. The force on one charge is the action and on the other is reaction and vice versa.

Problem 2: If, 25 C of charge is determined to pass through a wire of any cross section in 50 s, what is the measure of current?

Solution: I = q/t = (25 C) /(50 s) = 0.5 C/s = 0.5 A.

Problem 3: The current flowing through a lamp is 0.2 A. If the lamp is switched on for one hour, what is the total electric charge that passes through the lamp?

Solution: I = q/t; q = I x t

1 hr = 1 x 60 x 60 s = 3600 s

q = I x t = 0.2 A x 3600 s = 720 C

Problem 4: The e.m.f of a cell is 1.5 V. What is the energy provided by the cell to drive 0.5 C. of charge around the circuit?

Solution: ɛ = 1.5 V and q = 0.5 C

ɛ = W/q; W = ɛ x q; Therefore, W = 1.5 x 0.5 = 0.75 J.

Problem 5: A charge of 2 x 10⁴ C flows through an electric heater. The amount of electrical energy converted into thermal energy is 5 x 10⁶ J. Compute the potential difference across the ends of the heater.

Solution: V = W/q that is 5 x 10⁶ J / 2 x 10⁴ C = 250 V

Difference between e.m.f and potential difference:

As both e.m.f and potential difference are measured in volt, they may appear the same. But they are not. The e.m.f refers to the voltage developed across the terminals of an electrical source when it does not produces current in the circuit. Potential difference refers to the voltage developed between any two points (even across electrical devices) in an electric circuit when there is current in the circuit.

The heating effect and the chemical effect experiments have to be performed only with a dc cell of around 9 V. Students at any cost should not use the main domestic electric supply which is a 220 V ac voltage. If it is used it will give a heavy electric shock leading to a severe damage to our body.

Extremely weak electric current is produced in the human body by the movement of charged particles. These are called synaptic signals. These signals are produced by electro-chemical process. They travel between brain and the organs through nervous system.

In India, the voltage and frequency of ac used for domestic purpose is 220 V and 50 Hz respectively where as in United States of America it is 110 V and 60 Hz respectively.

Resistance of a dry human body is about 1,00,000 ohms. Because of the presence of water in our body the resistance is reduced to few hundred ohms. Thus, a normal human body is a good conductor of electricity. Hence, precautions are required while doing electrical work.

Choose the best answers:

1. In current electricity, a positive charge refers to

(a) Presence of electron

(b) Presence of proton

(c) Absence of electron

(d) Absence of proton

2. Rubbing of comb with hair

(a) Creates electric charge

(b) Transfers electric charge

(c) Either (a) or (b)

(d) Neither (a) nor (b)

3. Electric field lines ______________ from positive charge and ___________ in negative charge.

(a) Start; Start

(b) Start; end

(c) Start; end

(d) end; end

4. Potential near a charge is the measure of it’s __________ to bring a positive charge at that point.

(a) Force

(b) Ability

(c) Tendency

(d) Work

5. Heating effect of current is called

(a) Joule heating

(b) Coulomb heating

(c) Voltage heating

(d) Ampere heating

6. In an electrolyte the current is due to the flow of

(a) Electrons

(b) Positive ions

(c) Both (a) and (b)

(d) Neither (a) nor (b)

7. Electroplating is an example for

(a) Heating effect

(b) Chemical effect

(c) Flowing effect

(d) Magnetic effect

8. Resistance of a wire depends on

(a) Temperature

(b) Geometry

(c) Nature of material

(d) All the above

Match the following:

1. Electric charge – ohm

2. Potential difference – ampere

3. Electric field – coulomb

4. Resistance – Newton per coulomb

5. Electric current – volt

State true or false. If false, correct the statement:

1. Electrically neutral means it is either zero or equal positive and negative charges.

2. Ammeter is connected in parallel in any electric circuit.

3. The anode in electrolyte is negative.

4. Current can produce magnetic field.

Fill in the blanks:

1. Electrons move from ____________ potential to ______________ potential.

2. The direction opposite to the movement of electron is called _____________ current.

3. The e.m.f of a cell is analogues to _____________ of a pipe line.

4. The domestic electricity in India is an ac with a frequency of ___________ Hz.

Answers:

Choose the best answers:

1. absence of proton 2. either (a) or (b) 3. start; end 4. Work 5. Joule heating 6. Electrons 7. chemical effect 8. All the above

Match the following:

1.Electric charge – coulomb

2.Potential difference- Volt

3.Electric field- newton per coulomb

4.Resistance- ohm

5.Electric current- Ampere

State true or false. If false, correct the statement:

1.True

2.False

Correct answer: Ammeter is connected in series in any electric circuit

3.False

Correct answer: The anode in electrolyte is positive

4.True

Fill in the blanks:

1. Higher, lower 2. Conventional 3. A pump 4. 50