Through a semiconductor, an electric current is due to drift off:

1. Free electrons

2. Free electrons and holes

3. Positive and negative ions

4. Protons

The specific resistance of all metals is most affected by :

1. Temperature

2. Pressure

3. Degree of illumination

4. Applied magnetic field

The positive temperature coefficient of resistance is for :

1. Carbon

2. Germanium

3. Copper

4. An electrolyte

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