Question 1
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
View Answer
Answer: Option B
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.
Question 2
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
View Answer
Answer: Option A
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.
Question 3
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
View Answer
Answer: Option B
Explanation:
Metals are nothing but electrical conductors. The energy gap of a conductor is very small and equal to 1 ev.
Question 4
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
View Answer
Answer: Option D
Explanation:
The energy gap (Eg) of an insulator is approximately equal to 15 ev.
Question 5
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
View Answer
Answer: Option A
Explanation:
Bismuth has low conductivity. The resistivity of iron is 1.29 × 10-6 Ω-m.
Question 6
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
View Answer
Answer: Option D
Explanation:
Silver has lowest conductivity. The resistivity of silver is 1.59 × 10-9 Ω-m.
Question 7
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
View Answer
Answer: Option A
Explanation:
The equation, λ = h/mv is known as de Broglie’s equation. This equation represents the wave-particle duality of an electron.
Question 8
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
View Answer
Answer: Option A
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.
Question 9
With an increase in temperature, the resistance of a semiconductor ____________
A. increases
B. decreases
C. remains Constant
D. first increases and then decreases
View Answer
Answer: Option B
Explanation:
Semiconductors have a negative temperature coefficient of resistance thus resistance increases with decreasing temperature.
Question 10
Measured using an Electrical Conductivity meter, what is the order of resistivity of superconducting materials?
A. 10-8
B. 1016
C. ∞
D. 0
View Answer
Answer: Option D
Explanation:
The resistivity of superconducting materials is 0 since they conduct all electricity and resist none of it. Metals have the resistivity of the order of 10-8 while that of insulators is of the order of 1016. Since maximum electricity is refused by super-insulators, their resistivity is ∞.
Question 11
The insulating capacity of material against high voltages is known as _______
A. Dielectric strength
B. Thermoelectricity
C. Electromechanical effect
D. Electrochemical effect
View Answer
Answer: Option A
Explanation:
The dielectric strength of a material is its insulating capacity against a high voltage. The process by which two dissimilar metals join and produce a voltage is known as thermoelectricity. The electrical effect in a material is the relation between electrical energy and chemical change (as in batteries) and that of electromechanical effect is in an electrically operated mechanical device (as radar).
Question 12
What is the attribute of a material which resists the flow of electricity known?
A. Conductivity
B. Thermoelectricity
C. Dielectric strength
D. Resistivity
View Answer
Answer: Option D
Explanation:
Resistivity is that attribute of a material which resists the flow of electricity, while conductivity is it’s reciprocal (or) opposite. The process by which two dissimilar metals join and produce a voltage is known as thermoelectricity. The dielectric strength of a material is its insulating capacity against voltage.
Question 13
What is the dielectric strength of mica?
A. 118 MV/m
B. 2000 MV/m
C. 3 MV/m
D. 1012 MV/m
View Answer
Answer: Option A
Explanation:
The dielectric strength of mica is 118 MV/m. It is generally measured at 20oC, where 1 MV/m equals 10 V/m. The dielectric strengths of diamond, air, and vacuum are 2000, and 10 in MV/m in that order.
Question 14
What is the electrical conductivity of Aluminum?
A. 6.3 * 107
B. 5.9 * 107
C. 3.5 * 107
D. 1 * 107
View Answer
Answer: Option C
Explanation:
The electrical conductivity of Aluminum is 3.5 * 107. The electrical conductivity of Silver, Copper, and Iron is 6.3 * 107, 5.9 * 107, and 1 * 107 in that order. The electrical conductivity is generally measured at 20oC.
Question 15
What is the electrical resistivity of Copper?
A. 1.59 * 10-8
B. 1.68 * 10-8
C. 2.65 * 10-8
D. 5.9 * 10-8
View Answer
Answer: Option B
Explanation:
The electrical resistivity of Copper is 1.68 * 10-8. The electrical resistivity of Silver, Aluminum, and Zinc is 1.59 * 10-8, 2.65 * 10-8, and 5.9 * 10-8 in that order. The electrical resistivity is generally measured at 20oC.
Question 16
What is the nature of the coefficient of resistance of an insulator?
A. Positive
B. Negative
C. Zero
D. Infinite
View Answer
Answer: Option D
Explanation:
The coefficient of resistance of an insulator and a semiconductor material is generally negative. It is usually positive for pure metals. Zero coefficient values can be obtained by alloying with a specific type of metals.
Question 17
Which of the following processes is not an application of thermoelectric effect?
A. Seebeck effect
B. Peltier effect
C. Thomson effect
D. Ettingshausen effect
View Answer
Answer: Option D
Explanation:
Seebeck, Peltier, and Thomson are three distinct effects which make up the thermoelectric effect. Ettingshausen effect, however, is a separate thermoelectric phenomenon like the Nernst effect.