physics : class12 Radio Wave Generation : Radio Waves : Electromagnetic Waves MCQ Questions and Answers
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Radio Wave Generation
MCQ questions and answers.
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MCQ Questions
1. Radio waves are generated when electric charges undergo what type of motion?
A.
Uniform motion in a straight line
B.
Oscillatory motion
C.
Circular motion at constant speed
D.
Random motion without acceleration
Correct Answer:
Oscillatory motion
Explanation:
An oscillating charge produces changing electric and magnetic fields, which spread outward as radio waves.
2. Which device is commonly used to generate high-frequency oscillations for producing radio waves?
A.
LC oscillator
B.
Step-down transformer only
C.
Galvanometer
D.
Electric fuse
Correct Answer:
LC oscillator
Explanation:
An LC oscillator produces electrical oscillations that can be supplied to an antenna to generate radio waves.
3. In a radio-wave transmitter, the oscillating current is supplied to which component to radiate radio waves?
A.
Antenna
B.
Voltmeter
C.
Rheostat only
D.
Battery casing
Correct Answer:
Antenna
Explanation:
An antenna carries rapidly alternating current and radiates the resulting electromagnetic energy as radio waves.
4. What is the main source of the changing electric field in a radio-wave generator?
A.
A steady current
B.
An oscillating charge or current
C.
A stationary charge
D.
A permanent magnet at rest
Correct Answer:
An oscillating charge or current
Explanation:
Oscillating charges and currents create changing electric fields, which are essential for generating radio waves.
5. A spark-gap transmitter generates radio waves mainly by producing what in its antenna?
A.
A steady direct current
B.
A rapidly varying current
C.
No electric current
D.
A constant magnetic field only
Correct Answer:
A rapidly varying current
Explanation:
The spark produces sudden electrical oscillations, causing a rapidly varying current in the antenna and radiation of radio waves.
6. In an LC oscillator used for radio-wave generation, energy transfers repeatedly between which two components?
A.
The inductor and capacitor
B.
The resistor and fuse
C.
The battery and switch only
D.
The voltmeter and ammeter
Correct Answer:
The inductor and capacitor
Explanation:
An LC oscillator generates electrical oscillations through the repeated exchange of energy between the capacitor's electric field and the inductor's magnetic field.
7. What happens when a radio-frequency alternating current flows through a suitable antenna?
A.
It produces radio waves
B.
It stops all electric fields
C.
It produces only a steady magnetic field
D.
It prevents electromagnetic radiation
Correct Answer:
It produces radio waves
Explanation:
A high-frequency alternating current in an antenna creates changing electric and magnetic fields that radiate as radio waves.
8. The frequency of radio waves generated by an LC oscillator depends mainly on which quantities?
A.
The inductance and capacitance
B.
The color and shape of the antenna only
C.
The mass of the connecting wires only
D.
The temperature of the room only
Correct Answer:
The inductance and capacitance
Explanation:
The oscillation frequency of an LC circuit is determined by its inductance and capacitance, and this sets the frequency of the generated radio waves.
9. Why is a high-frequency alternating current used in radio-wave generation?
A.
To produce rapidly changing electric and magnetic fields
B.
To keep the charge completely stationary
C.
To eliminate oscillations in the antenna
D.
To convert the antenna into an insulator
Correct Answer:
To produce rapidly changing electric and magnetic fields
Explanation:
Rapidly changing currents create changing fields that can detach from the antenna and propagate as radio waves.
10. Which condition is necessary for an antenna to radiate radio waves effectively?
A.
The current in it must vary with time
B.
The current must remain exactly constant
C.
The antenna must contain no electric charges
D.
The antenna must be disconnected from the oscillator
Correct Answer:
The current in it must vary with time
Explanation:
A time-varying current produces changing electric and magnetic fields, enabling the antenna to radiate radio waves.
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