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

The positive temperature coefficient of resistance is for :

(1) Carbon

(2) Germanium

(3) Copper

(4) An electrolyte