# MCQs on Electrical Properties of Materials

1 - Question

Which of the following is the de Broglie’s equation (λ = wavelength, v = velocity, m = mass, h = Planck’s constant)?
a) λ = h/mv
b) λ = h/m
c) λ = h/v
d) λ = mv/h
Explanation: The equation, λ = h/mv is known as de Broglie’s equation. This equation represents the wave-particle duality of an electron.

2 - Question

With an increase in the mean free path of electrons, materials conductivity ____________
a) increases
b) decreases
c) remains constant
d) first increases and then decreases
Explanation: Conductivity of a material increases with an increase in the mean free path of electrons. Mean free path is nothing but the average distance travelled by an electron between two successive collisions.

3 - Question

What is the resistivity of silver (in Ohm-m) at room temperature?
a) 1.59 × 10-2
b) 1.59 × 10-3
c) 1.59 × 10-5
d) 1.59 × 10-9
Explanation: Silver has lowest conductivity. The resistivity of silver is 1.59 × 10-9 Ω-m. advertisement

4 - Question

What is the resistivity of iron (in Ohm-m) at room temperature?
a) 9.71 × 10-2
b) 9.71 × 10-8
c) 9.71 × 10-5
d) 9.71 × 10-9
Explanation: Iron has medium conductivity. The resistivity of iron is 9.71 × 10-8 Ω-m.

5 - Question

What is the resistivity of bismuth (in Ohm-m) at room temperature?
a) 1.29 × 10-6
b) 1.29 × 10-3
c) 1.29 × 10-5
d) 1.29 × 10-9
Explanation: Bismuth has low conductivity. The resistivity of iron is 1.29 × 10-6 Ω-m.

6 - Question

What is the energy gap (Eg) of an insulator?
a) Eg < 3 ev
b) Eg < 1 ev
c) Eg < 0 ev
d) Eg > 3 ev
Explanation: The energy gap (Eg) of an insulator is approximately equal to 15 ev.

7 - Question

What is the energy gap (Eg) of a metal?
a) Eg < 3 ev
b) Eg < 1 ev
c) Eg > 1 ev
d) Eg > 3 ev
Explanation: Metals are nothing but electrical conductors. The energy gap of a conductor is very small and equal to 1 ev.

8 - Question

If a copper wire of 200 m length having 0.44mm diameter has resistance of 20 Ohm, then find its specific resistance (in Ohm-m).
a) 1.520 × 10-8
b) 1.520 × 10-7
c) 1.520 × 10-6
d) 1.520 × 10-5
Explanation: A = 3.14×d2/4 and resistivity = R×A/l, where ‘A’ is the area of cross section of wire, ρ is specific resistance, R = resistance, d = diameter, l = length. Thus, A = 3.14×d2/4 = 3.14×(0.44)2/4 = 0.152 mm2, resistivity = R×A/l = (20×0.152/200) × 10-6 = 1.520 × 10-8.

9 - Question

If a copper wire of 10 m length having 0.44mm diameter has resistance of 2 Ohm, then what will be the specific resistance (in Ohm-m)?
a) 1.520 × 10-8
b) 3.041 × 10-8
c) 1.520 × 10-6
d) 1.520 × 10-5
Explanation: A = 3.14×d2/4 and resistivity = R×A/l, where ‘A’ is the area of cross section of wire, ρ is specific resistance, R = resistance, d = diameter, l = length. Thus, A = 3.14×d2/4 = 3.14×(0.44)2/4 = 0.152 mm2, resistivity = R×A/l = (2×0.152/10) × 10-6 = 3.041 × 10-8.

10 - Question

With an increase in temperature, the resistance of a semiconductor ____________
a) increases
b) decreases
c) remains Constant
d) first increases and then decreases