Electromagnetic Theory Questions and Answers – Brewster Angle

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

1. Brewster angle is valid for which type of polarisation?
a) Perpendicular
b) Parallel
c) S polarised
d) P polarised
View Answer

Answer: b
Explanation: The parallel polarisation of the electromagnetic waves is possible only when the transmission occurs at the Brewster angle.
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2. The Brewster angle is expressed as
a) Tan-1(n)
b) Tan-1(n1/n2)
c) Tan-1(n2/n1)
d) Tan (n)
View Answer

Answer: c
Explanation: The tangent of the Brewster angle is the ratio of the refractive indices of the second medium to that of the first medium. It is given by tan θb= n2/n1. Thus the Brewster angle will be θb = tan-1(n2/n1).

3. The refractive index of a material with permittivity 16 is given by
a) 16
b) 256
c) 4
d) 8
View Answer

Answer: c
Explanation: The refractive index is the square root of the permittivity. Thus n = √ε. Given that ε = 16, we get refractive index as n = 4. It has no unit.
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4. The reflection coefficient in the wave propagation when it is transmitted with the Brewster angle is
a) 0
b) 1
c) -1
d) Infinity
View Answer

Answer: a
Explanation: Brewster angle propagation refers to complete transmission. The wave transmitted at the Brewster angle will be completely transmitted without reflection. Thus the reflection coefficient will be zero.

5. The transmission coefficient of a wave propagating in the Brewster angle is
a) 0
b) 1
c) -1
d) Infinity
View Answer

Answer: b
Explanation: The transmission coefficient is the reverse of the reflection coefficient. At Brewster angle, the reflection will be zero. Thus the transmission is T = 1-R. Since R = 0, T = 1. It is to be noted that T and R lies in the range of 0 to 1.
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6. A circularly polarised wave transmitted at the Brewster angle will be received as linearly polarised wave. State True/False
a) True
b) False
View Answer

Answer: a
Explanation: The Brewster angle is said to be the polarisation angle. When a circularly polarised wave is incident at the Brewster angle, the resultant wave will be linearly polarised.

7. An elliptically polarised wave transmitted at the Brewster angle will be received as an elliptically polarised wave. State True/False
a) True
b) False
View Answer

Answer: b
Explanation: Any polarised wave transmitted at the Brewster angle will be linearly polarised. It can be a parallel, perpendicular, circular or elliptical polarisation. The resultant wave is always linearly polarised. This is the reason why the Brewster angle is called polarisation angle.
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8. Find the Brewster angle of a wave transmitted from a medium of permittivity 4 to a medium of permittivity 2.
a) 35.26
b) 53.62
c) 26.35
d) 62.53
View Answer

Answer: a
Explanation: The Brewster angle is given by θb = tan-1(n2/n1), where n = √ε. Thus we can express the formula in terms of permittivity as θb = tan-1√ (ε 2/ε 1). Here ε1 = 4 and ε2 = 2. Thus we get θb = tan-1√ (2/4) = tan-1(0.707) = 35.26 degree.

9. Find the ratio of refractive index of medium 2 to that of medium 1, when the Brewster angle is 60 degree.
a) 0.707
b) 1.5
c) 0.866
d) 1.732
View Answer

Answer: d
Explanation: The tangent of the Brewster angle is the ratio of the medium 2 permittivity to the medium 1 permittivity. Thus tan θb = (n2/n1). Given that θb = 60 degree, the ratio n2/n1 will be tan 60 = 1.732.
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10. The Brewster angle is the angle of
a) Incidence
b) Reflection
c) Refraction
d) Transmission
View Answer

Answer: a
Explanation: The Brewster angle is the angle of incidence at which complete transmission of the electromagnetic wave occurs.

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