Electromagnetic Spectrum(Radio Waves, Microwaves, Infrared, Visible, Ultraviolet. X-rays. Gamma Rays) NEET Questions

Physics - Electromagnetic Waves

Electromagnetic Spectrum(Radio Waves, Microwaves, Infrared, Visible, Ultraviolet. X-rays. Gamma Rays) MCQ Questions


13.
Which of the following is NOT a use of RADIO WAVES?
A.
Radar systems for aircraft detection and navigation
B.
AM and FM radio broadcasting
C.
Television signals and satellite communication
D.
Medical X-ray imaging of internal body organs
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ANSWER :
D. Medical X-ray imaging of internal body organs
14.
AM radio uses wavelengths of approximately 200–550 m (frequencies 540 kHz–1.5 MHz). These waves can travel around the Earth beyond the horizon because they are:
A.
Reflected by the ionosphere (a layer of ionised gas 60–1000 km above Earth's surface) back to the ground
B.
Diffracted around tall buildings only
C.
Absorbed and re-emitted by clouds
D.
Refracted by the atmosphere due to temperature gradients
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ANSWER :
A. Reflected by the ionosphere (a layer of ionised gas 60–1000 km above Earth's surface) back to the ground
15.
Frequency Modulation (FM) radio operates in the frequency range:
A.
470–890 MHz (UHF TV band)
B.
540–1600 kHz (AM band)
C.
2–4 GHz (microwave band)
D.
88–108 MHz (wavelength ≈ 2.78–3.41 m) — VHF (Very High Frequency) band
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ANSWER :
D. 88–108 MHz (wavelength ≈ 2.78–3.41 m) — VHF (Very High Frequency) band
16.
The wavelength range of MICROWAVES is approximately:
A.
1 nm to 400 nm (UV range)
B.
700 nm to 1 mm (IR range)
C.
1 mm to 1 m (10⁻³ m to 1 m); frequency range: 300 MHz to 300 GHz
D.
10⁻¹⁰ m to 10⁻⁸ m (X-ray range)
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ANSWER :
C. 1 mm to 1 m (10⁻³ m to 1 m); frequency range: 300 MHz to 300 GHz
17.
Microwave ovens heat food by which mechanism?
A.
Radiation from a hot glowing element inside the oven heats food by infrared
B.
The 2.45 GHz microwave radiation causes polar water molecules (H₂O) to rotate rapidly, generating heat throughout the food by molecular friction
C.
UV radiation from the magnetron sterilises and heats food simultaneously
D.
Microwaves cause nuclear reactions within food molecules
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ANSWER :
B. The 2.45 GHz microwave radiation causes polar water molecules (H₂O) to rotate rapidly, generating heat throughout the food by molecular friction
18.
Which device generates the microwaves in a microwave oven?
A.
A klystron amplifier — used only in radar systems
B.
A photomultiplier tube — converts photons to electric current
C.
A magnetron — a vacuum tube that generates microwaves by controlling the movement of electrons in a magnetic field
D.
A laser — stimulated emission from an excited gas medium
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ANSWER :
C. A magnetron — a vacuum tube that generates microwaves by controlling the movement of electrons in a magnetic field