Manufacturing Processes Questions and Answers Part-12

1. What is the energy gap (Eg) of a metal?
a) Eg < 3 ev
b) Eg < 1 ev
c) Eg < 0 ev
d) Eg < 2 ev

Answer: b
Explanation: Metals are nothing but electrical conductors. The energy gap of a conductor is very small and equal to 1 ev.

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

Answer: 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.

3. 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

Answer: 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.

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

Answer: b
Explanation: Semiconductors have a negative temperature coefficient of resistance; thus resistance increases with decreasing temperature.

5. Which of the following parameter is used to assess the magnetic ability of a material?
a) Magnetic flux density
b) Magnetization
c) Magnetic dipole moment
d) Susceptibility

Answer: d
Explanation: Magnetic susceptibility is a measure to quantify the ability of a material to undergo magnetization in an applied magnetic field. It is the ratio of magnetization (M) to the applied magnetic field intensity (H).

6. For a diamagnetic material, which of the following statement is correct?
a) Magnetic susceptibility < 0
b) Magnetic susceptibility > 0
c) Magnetic susceptibility = 0
d) Magnetic susceptibility = 1

Answer: a
Explanation: Diamagnetic materials are those which repel magnetic field and hence their magnetic susceptibility (χ) is negative.

7. For a diamagnetic material, which of the following statement is correct (μr = relative permeability)?
a) μr > 2
b) μr < 1
c) μr > 1
d) μr = 1

Answer: b
Explanation: A diamagnetic material has a constant relative permeability (μr) slightly less than 1.

8. For a paramagnetic material, which of the following statement is correct?
a) Magnetic susceptibility < 0
b) Magnetic susceptibility > 0
c) Magnetic susceptibility = 0
d) Magnetic susceptibility = -1

Answer: b
Explanation: Magnetic susceptibility (χ) is very small positive quantity for a paramagnetic material.

9. For a paramagnetic material, which of the following statement is correct (μr = relative permeability)?
a) μr = 0
b) μr < 1
c) μr > 1
d) μr < 0

Answer: c
Explanation: A paramagnetic material has a constant relative permeability (μr) slightly greater than 1.

10. What is the curie temperature of iron (in kelvin scale)?
a) 2195 K
b) 495 k
c) 895 k
d) 1095 K

Answer: d
Explanation: The curie temperature of iron is about 1095K. It changes its magnetic behaviour from ferromagnetic to paramagnetic.