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

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

The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter, the change in the resistance of the wire will be :

1. 300%

2. 200%

3. 100%

4. 50%

Express which of the following setups can be used to verify Ohm’s law 

1.
2.
3.
4.