Electromagnetic Theory Questions and Answers – Magnostatic Energy

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This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Magnetostatic Energy”.

1. Find the induced EMF in an inductor of 2mH and the current rate is 2000 units.
a) 4
b) -4
c) 1
d) -1
View Answer

Answer: b
Explanation: The induced emf is given by e = -Ldi/dt. Put L = 2 x 10-3 and di/dt = 2000 in the equation. We get e = -2 x 10-3 x 2000 = -4 units.
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2. Find the work done in an inductor of 4H when a current 8A is passed through it?
a) 256
b) 128
c) 64
d) 512
View Answer

Answer: b
Explanation: The work done in the inductor will be W = 0.5 x LI2. On substituting L = 4 and I = 8, we get, W = 0.5 x 4 x 82 = 128 units.

3. Find the inductance of a material with 100 turns, area 12 units and current of 2A in air.
a) 0.75mH
b) 7.5mH
c) 75mH
d) 753mH
View Answer

Answer: a
Explanation: The inductance of any material(coil) is given by L = μ N2A/I. On substituting N = 100, A = 0.12 and I = 2, we get L = 4π x 10-7 x 1002 x 0.12/2 = 0.75 units.
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4. Calculate the magnetic energy when the magnetic intensity in air is given as 14.2 units(in 10-4 order)
a) 1.26
b) 2.61
c) 6.12
d) 1.62
View Answer

Answer: a
Explanation: The magnetic energy is given by E = 0.5 μ H2. Put H = 14.2 and in air μ = 4π x 10-7, we get E = 0.5 x 4π x 10-7 x 14.22 = 1.26 x 10-4 units.

5. Calculate the magnetic energy when the magnetic flux density is given by 32 units(in 108 order)
a) 4.07
b) 7.4
c) 0.47
d) 7.04
View Answer

Answer: a
Explanation: The magnetic energy is given by E = 0.5 μ H2 and we know that μH = B. On substituting we get a formula E = 0.5 B2/μ. Put B = 32 and in air μ = 4π x 10-7, we get E = 0.5 x 322/4π x 10-7 = 4.07 x 108 units.
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6. Calculate the energy when the magnetic intensity and magnetic flux density are 15 and 65 respectively.
a) 755
b) 487.5
c) 922
d) 645
View Answer

Answer: b
Explanation: The magnetic energy can also be written as E = 0.5 μH2 = 0.5 BH, since B = μH. On substituting B = 65 and H = 15 we get E = 0.5 x 65 x 15 = 487.5 units.

7. Find the inductance when the energy is given by 2 units with a current of 16A.
a) 15.6mH
b) 16.5mH
c) 16.8mH
d) 15.8mH
View Answer

Answer: a
Explanation: The energy stored in an inductor is given by E = 0.5 LI2. To get L, put E = 2 and I = 16 and thus L = 2E/I2 = 2 x 2/162 = 15.6mH.
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8. Find the power of an inductor of 5H and current 4.5A after 2 seconds.
a) 25.31
b) 50.62
c) 102.4
d) 204.8
View Answer

Answer: a
Explanation: The energy stored in an inductor is given by E = 0.5 LI2. Thus, put L = 5 and I = 4.5 and we get E = 0.5 x 5 x 4.52 = 50.625 units To get power P = E/t = 50.625/2 = 25.31 units.

9. Find the turns in an solenoid of inductance 23.4mH , current 2A and area 15cm.
a) 900
b) 400
c) 498
d) 658
View Answer

Answer: c
Explanation: The inductance of any material(coil) is given by L = μ N2A/I.
Put L = 23.4 x 10-3, I = 2 and A = 0.15, we get N as 498 turns.
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10. The energy of a coil depends on the turns. State True/False.
a) True
b) False
View Answer

Answer: a
Explanation: The inductance is directly proportional to square of the turns. Since the energy is directly proportional to the inductance, we can say both are dependent on each other.

Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
To practice all areas of Electromagnetic Theory, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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