The electric intensity $E,$ current density $j$ and specific resistance $k$ are related to each other by the relation:
1. $E = j/k$
2. $E = jk$
3. $E = k/j$
4. $k = j E$

The resistance of a wire of uniform diameter d and length L is R. The resistance of another wire of the same material but diameter 2d and length 4L will be :

1. 2R

2. R

3. R/2

4. R/4

There is a current of 1.344 amp in a copper wire whose area of cross-section normal to the length of the wire is 1 mm². If the number of free electrons per cm³ is 8.4 × 10²², then the drift velocity would be :

1. 1.0 mm/sec

2. 1.0 m/sec

3. 0.1 mm/sec

4. 0.01 mm/sec

An electric wire of length ‘I’ and area of cross-section a has a resistance R ohms. Another wire of the same material having the same length and area of cross-section 4a has a resistance of :

1. 4R

2. R/4

3. R/16

4. 16R

If $n$, $e$, $\tau$ and $m$ respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length $l$ and area of cross-section $A$ will be:
1. $\frac{ml}{ne^2\tau A}$
2. $\frac{m\tau^2A}{ne^2l}$
3. $\frac{ne^2\tau A}{2ml}$
4. $\frac{ne^2 A}{2m\tau l}$

The relaxation time in conductors :

1. Increases with the increase in temperature

2. Decreases with the increase in temperature

3. It does not depend on the temperature

4. All of the sudden changes at 400 K

Which of the following has a negative temperature coefficient of resistance?

1. C

2. Fe

3. Mn

4. Ag

The reciprocal of resistance is :

1. Conductance

2. Resistivity

3. Voltage

4. None of the above

A solenoid is at the potential difference of $60~\text V$ and the current flows through it is $15~\text A$ then the resistance of the coil will be:
1. $4~\Omega$
2. $8~\Omega$
3. $0.25~\Omega$
4. $2~\Omega$