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

The resistivity of a wire :

Drift velocity $v_d$ varies with the intensity of the electric field as per the relation:
1. $v_{d} \propto E$
2. $v_{d} \propto \frac{1}{E}$
3. $v_{d}= \text{constant}$
4. $v_{d} \propto E^2$

In a conductor 4 coulombs of charge flows for 2 seconds. The value of electric current will be :

1. 4 volts

2. 4 amperes

3. 2 amperes

4. 2 volts

The specific resistance of a wire is ρ, its volume is 3 m³ and its resistance is 3 ohms, then its length will be 

1. $\sqrt{\frac{1}{\rho }}$

2. $\frac{3}{\sqrt{\rho }}$

3. $\frac{1}{\rho }\sqrt{3}$

4. $\rho \sqrt{\frac{1}{3}}$ 

When a piece of aluminum wire of finite length is drawn through a series of dies to reduce its diameter to half its original value, its resistance will become :

1. Two times

2. Four times

3. Eight times

4. Sixteen times

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