CBSE
Multiple Choice QuestionsAssertion: In a communication system based on amplitude modulation the modulation index is kept <1.
Reason: It ensures minimum distortion of signal.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Voltage of modulating wave of 5 V with 10 MHz frequency was superimposed on carrier wave of frequency 20 MHz and voltage 20 V then the modulation index is
0.25
1.25
2.43
64.0
Assertion: In the transmission of long distance radio signals, short wave band is used.
Reason: In shorter wavelength, attenuation is very less.
If both assertion and reason are true and reason is correct the explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Assertion: Communication in UHF/VHF regions can be established by space wave or tropospheric wave.
Reason: Communication in UHF/VHF regions is limited to line of sight distance
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false.
Given below is the circuit diagram of an AM demodulator. For good demodulation of AM signal of carrier frequency f, the value of RC should be
RC = 1/f
RC < 1/f
RC ≥ 1/f
RC >> 1/f
The area covered by a transmitting antenna of height 50 m is
320 km2
1440 km2
640 km2
120 km2
Assertion: Electromagnetic waves with frequencies smaller than the critical frequency of ionosphere are used for communication using sky wave propagation.
Reason: The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency.
If both assertion and reason are true and reason is the correct explanation of the assertion
If both assertion and reason are true but reason is not the correct explanation ofthe assertion
If assertion is true, but reason is false
Both assertion and reason are false statements
For skywave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere?
∼ 1.2 × 1012 m-3
∼ 106 m-3
∼ 1014 m-3
∼ 1022 m-3
Transmission lines transmit a voltage of V volt to our houses from power stations, then the power P supplied by them is proportional to
V
V2
If the highest modulating frequency of the wave is 5 kHz, the number of stations that can be accomodated in a 150 kHz bandwidth ?
15
10
5
None of these
