The specific resistance of all metals is most affected by :

1. Temperature

2. Pressure

3. Degree of illumination

4. Applied magnetic field

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. \(\frac{ne^2 A}{2m\tau l}\)

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

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

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 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. \(k = j E\)

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