Class XII Physics Communication Systems 2

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Question 1

A signal of frequency 20 kHz and peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1.2 MHz and peak voltage 25 Volts. Choose the correct statement.

• AModulation index=5, side frequency bands are at 1400 kHz and 1000 kHz
• BModulation index=5, side frequency bands are at 21.2 kHz and 18.8 kHz
• CModulation index=0.8, side frequency bands are at 1180 kHz and 1220 kHz
• DModulation index=0.2, side frequency bands are at 1220 kHz and 1180 kHz

Question 2

In general, which of the following statement is false regarding electromagnetic waves?

• AMay be a function of time only
• BConsists of sinusoidal time varying electric and magnetic fields
• CAccelerated charge is responsible for EM wave production
• DIn EM waves electric and magnetic fields are perpendicular to each other

Question 3

Magnetic field in a plane electromagnetic wave is given by

Expression for corresponding electric field will be:
Where c is speed of light.

• A
• B
• C
• D

Question 4

If the electric field component of an electromagnetic wave which propagates in free space is E= (40az+20ax) cos (t+2z-y)V/m then the magnetic field component is

• AH=-17.44 cos (1.342x 10^9+2y-z) ax
• BH=-27.44 cos (1.342x 10^9+2y-z) ay
• CH=-17.44 cos (1.342x 10^9+y-2z) ax
• DH=17.44 cos (1.342x 10^9+y-2z) az

Question 5

If the electric field component of an electromagnetic wave which propagates in free space is
E= 10ax V/m then the wavelength of the wave is

• A8.46m
• B7.13m
• C17.4m
• D9.42 m

Question 6

An electromagnetic wave has the magnetic field component as H = 50 cos (10^8t-7x) ay mA/m. The direction of propagation of wave is

• A+z direction
• B-z direction
• C+x direction
• D–x direction

Question 7

If a 24 V/m electric field of frequency 4.0 x 10¹⁰ Hz oscillates sinusoidally in a plane electromagnetic wave, then the total average energy density of the wave is

• A1.0 x 10^-8 J/m³
• B0.25 x 10^-8 J/m³
• C1.6 x 10^-8 J/m³
• D1.5 x 10^-8 J/m³

Question 8

Consider telecommunication through optical fibres. Which of the following statements is not true?

• AOptical fibres can be of graded refractive index.
• BOptical fibres are subject to electromagnetic interference from outside.
• COptical fibres have extremely low transmission loss.
• DOptical fibres may have homogeneous core with a suitable cladding

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