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

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.

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

Explanation: The work done in the inductor will be W = 0.5 x LI

^{2}. On substituting L = 4 and I = 8, we get, W = 0.5 x 4 x 8

^{2}= 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

Explanation: The inductance of any material(coil) is given by L = μ N

^{2}A/I. On substituting N = 100, A = 0.12 and I = 2, we get L = 4π x 10

^{-7}x 100

^{2}x 0.12/2 = 0.75 units.

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

Explanation: The magnetic energy is given by E = 0.5 μ H

^{2}. Put H = 14.2 and in air μ = 4π x 10

^{-7}, we get E = 0.5 x 4π x 10

^{-7}x 14.2

^{2}= 1.26 x 10

^{-4}units.

5. Calculate the magnetic energy when the magnetic flux density is given by 32 units(in 10^{8} order)

a) 4.07

b) 7.4

c) 0.47

d) 7.04

View Answer

Explanation: The magnetic energy is given by E = 0.5 μ H

^{2}and we know that μH = B. On substituting we get a formula E = 0.5 B

^{2}/μ. Put B = 32 and in air μ = 4π x 10

^{-7}, we get E = 0.5 x 32

^{2}/4π x 10

^{-7}= 4.07 x 10

^{8}units.

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

Explanation: The magnetic energy can also be written as E = 0.5 μH

^{2}= 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

Explanation: The energy stored in an inductor is given by E = 0.5 LI

^{2}. To get L, put E = 2 and I = 16 and thus L = 2E/I

^{2}= 2 x 2/16

^{2}= 15.6mH.

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

Explanation: The energy stored in an inductor is given by E = 0.5 LI

^{2}. Thus, put L = 5 and I = 4.5 and we get E = 0.5 x 5 x 4.5

^{2}= 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

Explanation: The inductance of any material(coil) is given by L = μ N

^{2}A/I.

Put L = 23.4 x 10

^{-3}, I = 2 and A = 0.15, we get N as 498 turns.

10. The energy of a coil depends on the turns. State True/False.

a) True

b) False

View Answer

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__.