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The correct option is (b) N = c/v

For explanation: The refractive index is DEFINED as the RATIO of the VELOCITY of light in a vacuum to its velocity in a specified medium. It is GIVEN by n = c/v. It is constant for a particular MATERIAL.

Right ANSWER is (a) NA = sin θa

Easy explanation: The numerical aperture is the measure of how MUCH LIGHT the fiber can collect. It is the sine of the acceptance angle, the angle at which the light must be transmitted in order to get MAXIMUM reflection. THUS it is given by NA = sin θa.

The correct ANSWER is (a) 9.11

To explain I would say: The transmission coefficient is the reverse of the reflection coefficient, i.e, T + R = 1. When T = 0.65, we get R = 0.35. THUS the RETURN loss RL = -20log R = -20log 0.35 = 9.11 DECIBEL.

Right choice is (C) 0.25

For explanation I would say: The return loss is given by RL = -20log R. The REFLECTION COEFFICIENT can be CALCULATED as R = 10^(-RL/20), by anti LOGARITHM property. For the given return loss RL = 12, we get R = 10^(-12/20) = 0.25.

The correct choice is (a) 4.8

Easy explanation: The POWER of an ANTENNA is GIVEN by Prad = Ia^2 Rrad, where Ia is the antenna current and Rrad is the radiation resistance. On SUBSTITUTING the given data, we get Rrad = Prad/Ia^2 = 120/5^2 = 4.8 ohm.

The CORRECT choice is (d) 0.75

The best I can explain: The VOLTAGE REFLECTION coefficient is the NEGATIVE of the CURRENT reflection coefficient. For a current reflection coefficient of -0.75, the voltage reflection coefficient will be 0.75.

Correct OPTION is (a) 13.01

The best I can explain: The ATTENUATION refers to the power loss. THUS the power loss is given by 20 units. The power loss in dB will be 10 LOG 20 = 13.01 decibel.

Right answer is (B) 2/3

For explanation I WOULD SAY: The ratio of the reflected to the incident voltage is the REFLECTION COEFFICIENT. It is given by R = 5/15 = 1/3. To get the transmission coefficient, T = 1 – R = 1 – 1/3 = 2/3.

The correct answer is (a) 12

The best EXPLANATION: The fraction of the TRANSMITTED to the incident POWER is given by the reflection coefficient. Thus Pref = (1-R^2) Pinc. On substituting the given data, we GET Pref = (1- 0.5^2) x 16 = 12 units. In other words, it is the remaining power after reflection.

Correct option is (d) 4

Explanation: The fraction of the REFLECTED to the incident power is given by the reflection COEFFICIENT. Thus Pref = R^2xPinc. On substituting the given data, we get Pref = 0.5^2 X 16 = 4 units.

The correct answer is (C) 196

Best EXPLANATION: The power of a wave is given by P = V^2/2Zo, where V is the generator VOLTAGE and ZO is the characteristic impedance. on substituting the given data, we get P = 140^2/(2×50) = 196 units.

The correct option is (c) √(μ/ε)

The EXPLANATION is: The intrinsic impedance is given by the ratio of square ROOT of the PERMITTIVITY to the permeability. Thus η = √(μ/ε) is the intrinsic impedance. In free space or air medium, the intrinsic impedance will be 120π or 377 OHMS.

The CORRECT answer is (a) True

The EXPLANATION is: In DIELECTRICS, the electric and magnetic FIELDS will be in phase or the phase difference between them is zero. This is due to the large attenuation which leads to increase in phase shift.

The correct ANSWER is (b) 3.14

To explain: The PHASE constant is GIVEN by β = 2π/λ. On SUBSTITUTING λ = 2 units, we get β = 2π/2 = π = 3.14 units.

Right choice is (a) C = 1/√(με)

For EXPLANATION I would say: The STANDARD relation between SPEED of light, PERMEABILITY and PERMITTIVITY is given by c = 1/√(με). The value in air medium is 3 x 10^8 m/s.

Right CHOICE is (a) 6

The explanation: The velocity of a wave is GIVEN by V = ω/β. To get ω, put v = 3 X 10^8 and β = 20. THUS ω = vβ = 3 x 10^8^ x 20 = 60 x 10^8 = 6 GHz.

Right ANSWER is (c) 0.02

For explanation I WOULD say: The PHASE constant of a dielectric is GIVEN by β = ω√(με). On substituting for ω = 6 x 10^6 , μ = 4π x 10^-7, ε = 8.854 x 10^-12 in air medium, we get the phase constant as 0.02 units.

Right CHOICE is (a) True

Easiest EXPLANATION: GOOD dielectrics attenuate the electromagnetic waves than any other material. Thus the attenuation CONSTANT of the dielectric will be non-zero, positive and large.

Right CHOICE is (a) Absolute permeability

Easiest EXPLANATION: The total permeability is the PRODUCT of the absolute and the relative permeability. In air medium, the relative permeability will be unity. Thus the total permeability is equal to the absolute permeability GIVEN by 4π X 10^-7 units.

The CORRECT option is (c) Conductivity

Explanation: There are no free charge carriers available in a DIELECTRIC. In other words, the charge carriers are PRESENT in the valence BAND, which is very difficult to start to conduct. Thus conduction is low in dielectrics. For pure dielectrics, the conductivity is assumed to be zero.

The CORRECT OPTION is (d) Minimum

The EXPLANATION: Dielectrics have poor conductivity. The loss tangent σ/ωε will be LOW in dielectrics. For perfect dielectrics, the loss tangent will be minimum.

Right option is (c) MOBILE transponder

The best EXPLANATION: The refrigerator, electric fan and RELAYS are electrical devices. They do not use ELECTROMAGNETIC energy as medium of energy transfer. The mobile transponder is an antenna, which uses the EM waves for communication with the SATELLITES.

Right answer is (a) √(ωμσ)

The BEST explanation: The propagation constant is the sum of the attenuation constant and the PHASE constant. In CONDUCTORS, the attenuation and phase constant both are same and it is GIVEN by √(ωμσ/2). Their sum will be √(ωμσ), is the propagation constant.

Right option is (a) V = √(2ω/μσ)

Best explanation: The velocity is the ratio of the frequency to the phase CONSTANT. In conductors, the phase constant is given by √(ωμσ/2). On SUBSTITUTING for β,ω in v, we GET v = √(2ω/μσ) UNITS.

Correct option is (d) 1/7

Explanation: The SKIN depth is the measure of the depth upto which an EM wave can penetrate through the conductor surface. It is the reciprocal of the ATTENUATION constant. On SUBSTITUTING for α = 7, we get δ = 1/α = 1/7 UNITS.

Correct OPTION is (d) 0.04

The explanation is: The phase CONSTANT and the attenuation constant are both the same in the CASE of conductors. Given that the attenuation constant is 0.04, implies that the phase constant is also 0.04.

Right answer is (c) Product of absolute and relative permeability

The BEST explanation: The total permeability is the product of the absolute and the relative permeability. For METALS or conductors, the relative permittivity is not UNITY. Thus the permittivity is the product of absolute and relative permeability.

Correct CHOICE is (a) Absolute permittivity

Easiest explanation: The total permittivity is the product of the absolute and the relative permittivity. For METALS or CONDUCTORS, the relative permittivity is unity. Thus the permittivity is SIMPLY the absolute permittivity.

Correct CHOICE is (b) 3 X 10^8

Explanation: In free space or air medium, the velocity of the wave propagating will be same as that of the LIGHT. Thus the velocity is the speed of light, V = C. It is given by 3 x 10^8m/s.

Right option is (b) Minimum ATTENUATION and maximum propagation

Best EXPLANATION: The free SPACE does not have any BARRIER for attenuation. Thus it enables minimum attenuation and maximum propagation. This technique is employed in line of sight COMMUNICATION.

Right ANSWER is (d) 377

To EXPLAIN: The INTRINSIC impedance is the SQUARE root of ratio of the permeability to the permittivity. In free SPACE, the permeability and the permittivity is same as the absolute permeability and permittivity respectively. This is due to unity permeability and permittivity in free space. Thus η = √(μ/ε), where absolute permeability is given by 4π x 10^-7 and absolute permittivity is given by 8.854 x 10^-12. The intrinsic impedance will be 377 ohms.

Right answer is (c) Zero

For EXPLANATION I WOULD say: As the charge carriers are not available in free space, the CONDUCTIVITY will be very low. For ideal cases, the conductivity can be taken as zero.

Right answer is (c) No magnetic or ELECTRIC energy is permitted in the medium

Best EXPLANATION: The ZERO PERMITTIVITY in an electric field refers to the ability of the field/medium to permit electric charges in it. SIMILARLY, zero permeability in a magnetic field refers to the ability of the field/medium to permit the magnetic energy into the field.

Right ANSWER is (C) Relative permittivity

Explanation: The relative permittivity is a constant for a PARTICULAR material. It is unity for free space or air. The absolute permittivity is a constant given by 8.854 x 10^-12 C/m2.

Right ANSWER is (c) Relative permeability

To explain: In free space or air medium, the relative permeability is also UNITY, like relative PERMITTIVITY. The absolute permeability is GIVEN by 4π x 10^-7 units.

Correct option is (a) 0

To EXPLAIN I would say: Free space is not a CONDUCTOR. Thus the CHARGE carrier in free space is ASSUMED to be zero. But the free space consists of particles or ions that GET ionized during conduction.

Right choice is (a) V > c

To elaborate: In waveguides, the PHASE velocity will always be GREATER than the SPEED of light. This enables the wave to PROPAGATE through the waveguide. Thus V > c is the required condition.

Right option is (C) PHASE CONSTANT β = ω√(με)

For explanation: The phase constant is represented as β. It is a complex QUANTITY REPRESENTING the constant angle of the wave propagated. It is given byβ = ω√(με).

The correct choice is (d) E and H

The BEST I can EXPLAIN: In DIELECTRICS, the electric and magnetic components E and H will be in phase with each other. This is due the variation in the permittivities and the permeabilities of the dielectric SURFACES. The phase difference between E and H will be 0.

Correct option is (d) Infinity

Best EXPLANATION: Metals are PURE conductors. Examples are iron, copper etc. Their CONDUCTIVITY will be very high. THUS the metal conductivity will be infinity. Practically the conductivity of conductors will be maximum.