NCERT Solutions for Class 12 Help.html Physics Part Ii Chapter 15 Communication Systems

Which mode of propagation is used by short wave broadcast services?

A carrier wave of peak voltage 15 V is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of 60%.

Give three reasons why the modulation of a message signal is necessary for long-distance transmission.

Show graphically an audio signal, a carrier wave and an amplitude modulated wave.

A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of

• 1000

• 10000

• 10

• 100

In a full wave rectifier circuit operating from 50 Hz mains frequency, the fundamental frequency in the ripple would be

• 50 Hz

• 25 Hz

• 100 Hz

• 70.7 Hz

A telephonic communication service is working at carrier frequency of 10 GHz. Only 10% of it is utilized for transmission. How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of 5 kHz?

• 2 x 10⁶

• 2 x 10⁵

• 2 x 10⁴

• 2 x 10⁵

A source emits electromagnetic waves of wavelength 3m. One beam reaches the observer directly and other after reflection from a water surface, travelling 1.5 m extra distance and with an intensity reduced to 1/4 as compared to intensity due to the direct beam alone. The resultant intensity will be.

• (1/4) fold

• (3/4) fold

• (5/4) fold

• (9/4) fold

A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of

• 1000

• 10000

• 10

• 100

What maximum frequency can be reflected from ionosphere?

• 5 MHz

• 6 GHz

• 5 KHz

• 500 MHz