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

A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/ quantities constant along the length of the conductor is/are :

(1) Current, electric field and drift speed

(2) Drift speed only

(3) Current and drift speed

(4) Current only

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

A wire of radius r has resistance R. If it is stretched to a radius of $\frac{3r}{4}$, its resistance becomes 

(1) $\frac{9R}{16}$

(2) $\frac{16R}{9}$

(3) $\frac{81R}{256}$

(4) $\frac{256R}{81}$

A copper wire has a square cross-section, 2.0 mm on a side. It carries a current of 8 A and the density of free electrons is 8 × 10²⁸ m^–3. The drift speed of electrons is equal to 

(1) 0.156 × 10^–3 m.s^–1

(2) 0.156 × 10^–2 m.s^–1

(3) 3.12 × 10^–3 m.s^–1

(4) 3.12 × 10^–2 m.s^–1

What length of the wire of specific resistance $48\times {10}^{-8}\Omega m$is needed to make the resistance of 4.2 Ω (diameter of wire = 0.4 mm) 

(1) 4.1 m

(2) 3.1 m

(3) 2.1 m

(4) 1.1 m

A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of 

(1) Each of these increases

(2) Each of these decreases

(3) Copper strip increases and that of germanium decreases

(4) Copper strip decreases and that of germanium increases