physics : class12 Frequency Modulation : Radio Waves : Electromagnetic Waves MCQ Questions and Answers
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Frequency Modulation
MCQ questions and answers.
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MCQ Questions
1. In frequency modulation, which property of the carrier wave is varied according to the message signal?
A.
Frequency
B.
Amplitude
C.
Speed
D.
Polarisation
Correct Answer:
Frequency
Explanation:
In frequency modulation, the frequency of the carrier wave changes in accordance with the instantaneous amplitude of the message signal.
2. In an FM signal, the amplitude of the carrier wave is ideally kept:
A.
Constant
B.
Increasing continuously
C.
Decreasing continuously
D.
Zero
Correct Answer:
Constant
Explanation:
In frequency modulation, the carrier frequency varies while its amplitude remains constant.
3. The frequency of an FM wave is highest when the modulating signal has:
A.
Its maximum positive amplitude
B.
Zero amplitude only
C.
Its maximum negative amplitude
D.
No variation
Correct Answer:
Its maximum positive amplitude
Explanation:
For a conventional FM signal, a positive maximum in the modulating signal produces the greatest increase in carrier frequency.
4. The frequency of an FM wave is lowest when the modulating signal has:
A.
Its maximum negative amplitude
B.
Its maximum positive amplitude
C.
Zero amplitude only
D.
Constant positive amplitude
Correct Answer:
Its maximum negative amplitude
Explanation:
A maximum negative value of the modulating signal produces the greatest decrease in the instantaneous carrier frequency.
5. In frequency modulation, the rate at which the carrier frequency changes is determined by the:
A.
Frequency of the modulating signal
B.
Amplitude of the carrier only
C.
Speed of light
D.
Polarisation of the carrier
Correct Answer:
Frequency of the modulating signal
Explanation:
The carrier frequency follows the variations of the modulating signal, so the modulating frequency determines how rapidly the carrier frequency changes.
6. The maximum departure of the instantaneous frequency from the carrier frequency is called:
A.
Frequency deviation
B.
Carrier amplitude
C.
Modulating period
D.
Signal wavelength
Correct Answer:
Frequency deviation
Explanation:
Frequency deviation is the maximum change in the instantaneous frequency of the carrier from its unmodulated value.
7. If the amplitude of the modulating signal is increased while other conditions remain unchanged, the frequency deviation in FM will:
A.
Increase
B.
Decrease to zero
C.
Remain exactly zero
D.
Become independent of the modulating signal
Correct Answer:
Increase
Explanation:
A larger modulating-signal amplitude produces a larger change in the instantaneous carrier frequency, increasing the frequency deviation.
8. If the frequency of the modulating signal is increased, the number of carrier-frequency variations per second will:
A.
Increase
B.
Decrease to zero
C.
Remain fixed at one
D.
Become unrelated to modulation
Correct Answer:
Increase
Explanation:
The carrier frequency follows the modulating signal, so a higher modulating frequency causes more frequency variations each second.
9. Which device is commonly used to produce frequency modulation by changing the carrier frequency?
A.
Frequency modulator
B.
Rectifier
C.
Transformer only
D.
Ammeter
Correct Answer:
Frequency modulator
Explanation:
A frequency modulator is designed to vary the carrier frequency in accordance with the message signal.
10. A major advantage of frequency modulation over amplitude modulation is that FM is less affected by:
A.
Amplitude noise
B.
Carrier frequency
C.
Message frequency
D.
Frequency deviation
Correct Answer:
Amplitude noise
Explanation:
Since information in FM is carried by frequency changes and the carrier amplitude is constant, amplitude noise has less effect on the received signal.
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