If a resistance coil is made by joining in parallel two resistances each of 20$\Omega$. An emf of 2V is applied across this coil for 100 seconds. The heat produced in the coil is

1. 20 J

2. 10 J

3. 40 J

4. 80 J

If I be the current limit of a fuse wire of length l and radius r, then select the appropriate relation

1. $I \alpha l$

2. $I \alpha r^2$

3. $I \alpha l^0$

4. $I \alpha r^0$

A current of 1 mA is flowing through a copper wire. How many electrons will pass a given point in one second  $\left[\mathrm{e} = 1.6 \times {10}^{-19} \mathrm{Coulomb}\right]$

1.  $6.25 \times {10}^{19}$

2.  $6.25 \times {10}^{15}$

3.  $6.25 \times {10}^{31}$

4.  $6.25 \times {10}^8$

The drift velocity of free electrons in a conductor is $v$ when a current $i$ is flowing in it. If both the radius and current are doubled, then the drift velocity will be:

The current $I$ as shown in the circuit will be:

A meter bridge is set up to determine unknown resistance $x$ using a standard $10~\Omega$ resistor. The galvanometer shows the null point when the tapping key is at a $52$ cm mark. End corrections are $1$ cm and $2$ cm respectively for end $A$ and $B$. Then the value of $x$ is:

      
1. $10.2~\Omega$
2. $10.6~\Omega$
3. $10.8~\Omega$
4. $11.1~\Omega$

The resistivity of iron is 1 × 10^–7 ohm – m. The resistance of iron wire of particular length and thickness is 1 ohm. If the length and the diameter of wire both are doubled, then the resistivity in ohm – m will be :

1. 1 × 10^–7

2. 2 × 10^–7

3. 4 × 10^–7

4. 8 × 10^–7