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 of \(60~\text V\) and the current flows through it is \(15~\text A\) then the resistance of the coil will be:
1. \(4~\Omega\)
2. \(8~\Omega\)
3. \(0.25~\Omega\)
4. \(2~\Omega\)

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