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The MCQs below are drawn from the Physics subject category.
Showing 1191–1200
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1191
The spectral energy distribution of the sun (temperature 6050 K) has a maximum at 4753 Å. The temperature of a star for which this maximum is at 9500 Å is
A. 24200 K
B. 3025 K
C. 12100 K
D. 6050 K
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Correct Option
Explanation
Using Wien's law (λ_max T = constant), doubling λ_max halves T; 9500 Å is about double 4753 Å, so T ≈ 6050/2 ≈ 3025 K.
1192
The frequency of radio waves is measured in
A. Centimeter
B. Hertz
C. Cycles
D. Per cycles
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Correct Option
Explanation
Frequency is measured in hertz (Hz), defined as cycles per second.
1193
Who explained the Franhofer lines in the spectrum of solar radiations?
A. Stefan
B. Kirchoff
C. Wein
D. Fraunhofer
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Correct Option
Explanation
Joseph von Fraunhofer identified and explained the dark lines (Fraunhofer lines) in the solar spectrum.
1194
A beam of monochromatic radiation falls on to a metal X and photoelectrons are emitted. The rate of emission of photoelectrons will be doubled if
A. radiation of double the frequency is used
B. radiation of double the wavelength is used
C. a beam of double the intensity is used
D. the thermodynamic temperature of the metal is increased
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Correct Option
Explanation
Photoelectron emission rate is proportional to the number of incident photons (intensity); doubling intensity doubles the photon flux and thus the emission rate.
1195
What for is a modulator circuit used?
A. To create sound waves
B. To transmit the signal
C. To eliminate carrier waves
D. To superpose the radio frequency signal on the carrier waves
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Correct Option
Explanation
A modulator superposes (imposes) the information signal onto the carrier wave for transmission.
1196
The velocity of electromagnetic radiation in free space is
A. 0 m s^-1
B. 3 × 10^10 m s^-1
C. 3 × 10^8 m s^-1
D. 310 m ×1
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Correct Option
Explanation
The speed of electromagnetic radiation in free space is approximately 3 × 10^8 m/s, so option C is correct.
1197
Molybdenum is used as a target element for production of X-rays because it is
A. an element having high thermal conductivity
B. a heavy element and can easily absorb high velocity electrons
C. a heavy element can easily deflect electrons
D. a heavy element with a high melting point
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Correct Option
Explanation
Molybdenum is chosen for some X-ray targets because its relatively high melting point and suitable characteristic X-ray energies make it practical for use.
1198
The infrared spectrum lies between
A. radiowave and microwave region
B. the ultraviolet and the X-ray region
C. the visible and ultra-violet region
D. the microwave and the visible region
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Correct Option
Explanation
Infrared frequencies are higher than microwaves but lower than visible light, so the IR region lies between microwave and visible regions.
1199
Which of the following is an example of band spectra?
A. Anomalous spectrum
B. Molecular spectra
C. Blackbody radiation spectrum
D. Atomic spectra
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Correct Option
Explanation
Molecular transitions often produce bands of closely spaced lines, resulting in band spectra.
1200
The shadow of the bones in X-ray photographic film appears lighter than the surrounding flesh due to:
A. Bones reflect greater amount of X-rays
B. Bones absorb less amount of X-rays
C. Bones totally reflect X-rays
D. Bones absorb greater amount of X-rays
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Correct Option
Explanation
Bones absorb more X-rays than flesh, so fewer X-rays reach the film behind bones, producing a lighter area.
