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, τ 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) $\frac{ml}{n{e}^2\tau A}$

(2) $\frac{m{\tau }^{2}A}{n{e}^{2}l}$

(3) $\frac{n{e}^2\tau A}{2ml}$

(4) $\frac{n{e}^{2}A}{2m\tau l}$ 

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 60 V and current flows through it is 15 ampere, then the resistance of coil will be :

(1) 4 Ω

(2) 8 Ω

(3) 0.25 Ω

(4) 2 Ω

All of the following statements are true except 

(1) Conductance is the reciprocal of resistance and is measured in Siemens

(2) Ohm's law is not applicable at very low and very high temperatures

(3) Ohm's law is applicable to semiconductors

(4) Ohm's law is not applicable to electron tubes, discharge tubes and electrolytes

The resistance of a discharge tube is :

(1) Ohmic

(2) Non-ohmic

(3) Both (1) and (2)

(4) Zero

σ₁ and σ₂ are the electrical conductivities of Ge and Na respectively. If these substances are heated, then

(1) Both σ₁ and σ₂ increase

(2) σ₁ increases and σ₂ decreases

(3) σ₁ decreases and σ₂ increases

(4) Both σ₁ and σ₂ decrease

Masses of 3 wires of same metal are in the ratio 1 : 2 : 3 and their lengths are in the ratio 3 : 2 : 1. The electrical resistances are in ratio

(1) 1 : 4 : 9

(2) 9 : 4 : 1

(3) 1 : 2 : 3

(4) 27 : 6 : 1