# Electricity

## Class 10 NCERT Science

### NCERT

1   What does an electric circuit mean?

##### Solution :

A continuous and closed path of an electric current is called an electric circuit. electric circuit consists of electric devices like switching devices, source of electricity, etc.

2   Define the unit of current.

##### Solution :

The unit of electric current is ampere (A).$1$A is defined as the flow of $1$C of charge through a wire in $1$ s of time.

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

##### Solution :

We know that charge is quantized i.e., Q = ne where n = number of electrons and e = charge of an electron , Therefore Given that$\\$ $Q=1C,e=1.6*10^{-19}C,n=?$$\\ On substitution the above values in Q = ne, We get,\\ 1C=n*1.6*10^{-19}=\\ \dfrac{1}{1.6*110^{-19}}=\\ 6.25*10^{18}$$\\$ $=6*10^{18}$ electrons$\\$ Therefore, $6*10^{18 }$electrons constitute one coulomb of charge.

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

##### Solution :

A source of electricity such as cell, battery, power supply, etc. helps to maintain a potential difference across a conductor.

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

##### Solution :

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 $1 V$.

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

##### Solution :

(a) Resistivity of iron $= 10.0 * 10^{-8} \Omega m$ $\\$ Resistivity of mercury $= 94.0 * 10^{-8 }\Omega m$ $\\$ 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 that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.