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## Class Ten Science Chapter 12 NCERT Solutions

#### Chapter12 : Electricity

Q.1. What does an electric circuit mean?

Ans. A continuous and closed path of an electric current is called an electric circuit. An electric circuit consists of electric devices, source of electricity and wires that are connected with help of a switch.

Q.2. Define the unit of current.

Ans. SI unit of electric current is ampere (A). If 1 coulomb of electric charge flows through a cross-section of wire for 1 second, then it would be equal to 1 ampere. So, 1 ampere = 1C 1s i.e. 1 A = 1 Cs–1

Q.3. Calculate the number of electrons constituting one coulomb of charge.

Ans. One electron possesses a charge of 1.6 × 10–19 C

Given q = 1 C, e = 1.6 × 10–19 C

n = ?

q = ne

n = q/e

Q.4. Name a device that helps to maintain a potential difference across a conductor.

Ans. Any source of electricity like a battery, cell, power supply, etc. help to maintain a potential difference across a conductor.

Q.5. What is meant by saying that the potential difference between two points is 1 V?

Ans. If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.

Q.6. How much energy is given to each coulomb of charge passing through a 6 V battery?

Ans. The energy given to each coulomb of charge is equal to the amount of work which is done in moving it.

Now we know that,

Potential difference = Work done/ Charge

∴ Work done = Potential difference × Charge

Charge = 1 C and Potential difference = 6 V (given)

∴ Work done = 6 × 1 = 6 J

Q.7. On what factors does the resistance of a conductor depend?

Ans. The resistance of a conductor depends upon the following factors.

(i) Length of the conductor. (ii) The cross-sectional area of the conductor.

(iii) The material of the conductor. (iv) The temperature of the conductor.

Q.8. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

Ans. The current will flow more easily through the thick wire. It is because the resistance of a conductor is inversely proportional to its area of cross-section. If thicker the wire, less is resistance and hence more easily the current flows.

Q.9. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

Ans. According to Ohm’s law

V = IR ⇒ I = V/R …(1)

Now Potential difference is decreased to half.

∴ New potential difference V′ = V/2

Resistance remains constant.

from Ohm’s law, I = V/R

Therefore, the amount of current flowing through the electrical component is reduced by half.

Q.10. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

Ans. The resistivity of an alloy is higher than the pure metal. Moreover, at high temperatures, the alloy does not melt readily. Hence, the coils of heating appliances such as electric toasters and electric irons are made of an alloy than a pure metal.

Q.11. Use the data in Table 1.1 to answer the following:

(a) Which among iron and mercury is a better conductor?

(b) Which material is the best conductor?

Table 1.1 Electrical resistivity of some substance at 20°

Ans. (a) Resistivity of iron = 10.0 × 10–8 Ω

Resistivity of mercury = 94.0 × 10–8 Ω

The resistivity of mercury is more than that of iron. This implies that iron is a better conductor than mercury.

(b) It can be observed from Table 1.1 that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.