# Electromagnetic Theory Questions and Answers – S and P Polarised Waves

This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “S and P Polarised Waves”.

1. The resultant electric field of a wave with Ex = 3 and Ey = 4 will be
a) 7
b) 1
c) 25
d) 5

Explanation: The resultant electric field of two electric components Ex and Ey is E = √(Ex2 + Ey2). On substituting for Ex = 3 and Ey = 4, we get E = 5 units.

2. In S polarisation, the electric field lies in the plane perpendicular to that of the interface. State True/False
a) True
b) False

Explanation: In the EM wave propagation, the electric and magnetic fields are perpendicular to each other. The S polarised wave is similar to the transverse magnetic (TM) wave, the electric field lies in the plane perpendicular to that of the interface.

3. In P polarisation, the electric field lies in the same plane as the interface. State True/False.
a) True
b) False

Explanation: In the EM wave propagation, the electric and magnetic fields are perpendicular to each other. The P polarised wave is similar to the transverse electric (TE) wave, the magnetic field lies in the plane perpendicular to that of the interface or the electric field lies in the same plane as the interface.

4. The group delay of a wave with phase constant 2.5 units and frequency of 1.2 radian/sec is
a) 3.7
b) 1.3
c) 3
d) 2.08

Explanation: The group delay is given by td = β/ω. On substituting for β = 2.5 and ω = 1.2, we get the group delay as td = 2.5/1.2 = 2.08 units.

5. The Brewster angle is valid for which type of polarisation?
a) S polarised
b) P polarised
c) Elliptical
d) Linear

Explanation: The Brewster angle is valid for perpendicular polarisation. The P polarised wave is also a type of perpendicular polarisation. In P polarisation, the electric field lies in the plane of the interface.

6. Find the reflection coefficient of a wave with an incident electric field of 5 units and reflected electric field of 2 units.
a) 2.5
b) 0.4
c) 0.8
d) 1.2

Explanation: The reflection coefficient is the ratio of the reflected electric field to the incident electric field. Thus τ = Er/Ei. On substituting for Ei = 5 and Er = 2, we get τ = 2/5 = 0.4(no unit).

7. The transmission coefficient of a wave with incident and transmitted electric field of 5 and 5 respectively is
a) 0
b) 1
c) 10
d) 5

Explanation: The transmission coefficient is the ratio of the transmitted electric field to the incident electric field. Thus T = Et/Ei. On substituting for Et = 5 and Ei = 5, we get T = 5/5 = 1(no unit). Simply, when the incident and transmitted field are same, no reflection occurs and the transmission is unity.

8. Find the relative permittivity of the medium having a refractive index of 1.6
a) 0.4
b) 2.56
c) 3.2
d) 4.8

Explanation: The refractive index is the square root of the relative permittivity. It is given by n = √εr. To get εr, put n = 1.6. We get εr = n2 = 1.62 = 2.56(no unit).

9. Calculate the transmission coefficient of a wave with a reflection coefficient of 0.6
a) 0.6
b) 1
c) 0
d) 0.4

Explanation: The transmission coefficient is the reverse of the reflection coefficient. Thus T + τ = 1. On substituting for τ = 0.6, we get T = 0.4. It has no unit.

10.The phase constant of a wave propagation with frequency of 35 radian/sec and time delay of 7.5 sec is
a) 4.66
b) 262.5
c) 46.6
d) 26.25

Explanation: The group delay expression is td = β/ω. To get β, put ω = 35 and td = 7.5. Thus we get β = td x ω = 7.5 x 35 = 262.5 units.

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