# Electromagnetic Theory Questions and Answers – Real Time Applications

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This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Real Time Applications”.

1. In a magnetic material, always there exist magnetic dipoles as well as monopoles. State True/False.
a) True
b) False

Explanation: A magnetic material possesses only magnetic dipoles. The absence of magnetic monopoles is indicated by the equation Div(B) = 0.

2. Find the total flux in a material of flux density 15 units in an area of 24 units.
a) 3.6
b) 7.2
c) 9.6
d) 5.4

Explanation: The total flux in a material is given by φ = ∫ B.dS. Put B= 15 and ∫dS = 0.24. On substituting, we get φ = 15 x 0.24 = 3.6 units.

3. Find the magnetic field intensity of a material with flux density of 24 units in air(in 106 order)
a) 19.09
b) 21
c) 25
d) 26.78

Explanation: The magnetic flux density is given by B = μ H. To get H, put B = 24 and μ = 4∏ x 10-7. Thus H = 24/4∏ x 10-7 = 19.09 x 106 units.
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4. Find the magnetic flux density when the vector potential is a position vector.
a) 1
b) 0
c) -1
d) ∞

Explanation: The magnetic flux density is given by B = Curl(A) and A = x i + y j + z k. The curl of the position vector A is i(0) – j(0) + k(0) = 0. Thus the flux density is also zero.

5. When the electric field travels in +x direction and the EM wave is travelling the –y direction, then the magnetic field will be travelling in which direction?
a) +z direction
b) –z direction
c) Either +z or –z direction
d) Does not travel

Explanation: The electric field and magnetic field will always travel perpendicular to each other and the EM wave will travel perpendicular to both these fields. In the given condition when E travels in +x direction and wave in –y direction, then the H field that is perpendicular to both components will be travelling in either +z or –z direction.

6. Inductance is present in semiconductor. State True/False.
a) True
b) False

Explanation: Inductance property exists only for pure conductors like coil, solenoid, toroid etc. It is not present in semiconductors.

7. Electromagnetic waves are longitudinal in nature. State True/False.
a) True
b) False

Explanation: Light and other electromagnetic radiations are transverse in nature as they travel at the same speed through a vacuum, such as through space. Such waves vibrate at right angles to the direction of propagation.

8. Identify the devices that do not use electromagnetic energy.
a) Television
b) Washing machine
c) Microwave oven
d) Mobile phones

Explanation: Television and mobile phones use the electromagnetic waves as signals. Microwave ovens generate electromagnetic waves (microwaves) for heating the food. Washing machine does not use any EM wave for its operation.

9. Find the flux density of a conductor in the square of the centre of the loop having current 3.14A and radius is 1.414m in air.
a) 8π x 10-7
b) 4π x 10-7
c) 6π x 10-7
d) 2π x 10-7

Explanation: The magnetic flux density of a conductor in the square of centre of the loop is given by B = 2√2 μo I/π R. Put I = 3.14 and R = 1.414, we get B = 2 x 1.414 x 4π x 10-7 x 3.14/π x 1.414 = 8π x 10-7 units.

10. Which type of flux will increase the inductance?
a) Series aiding
b) Series opposing
c) Shunt aiding
d) Shunt opposing

Explanation: The series aiding flux will give maximum inductance to a circuit compared to any other fluxing techniques. This is because all the individual and mutual inductances will get added.

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