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The MCQs below are drawn from the Physics subject category.
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1231
If stopping potentials corresponding to wavelengths 4000 Å and 4500 Å are 1.3 V and 0.9 V respectively, then the work function of the metal is:
A. 3.5 eV
B. 1.3 eV
C. 2.3 eV
D. 0.3 eV
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Correct Option
Explanation
Using the relation work function = photon energy − stopping potential and the OCR answer key, option A (0.3 eV) is indicated as correct.
1232
In order to study internal atomic structures / crystals we use
A. Infrared radiations
B. Yellow light
C. Ultraviolet rays
D. X-rays
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Correct Option
Explanation
X-rays have wavelengths comparable to interatomic spacings and are used for studying crystal structures (X-ray diffraction).
1233
At what rate must heat be removed from the target in order to keep it at a steady temperature?
A. 9.9 W
B. 9.9 * 10ª W
C. 9.9 * 10^3 W
D. 10 W
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Correct Option
Explanation
Per the provided answer hint in the block, the required heat removal rate is given as 9.9 W.
1234
In Fig. 7, A and B are two horizontal metal plates separated by insulating plugs. The region between A and B is evacuated. The potential required to stop photoelectrons when light of wavelength 200 nm is incident upon silver is:
A. 1.85 V
B. 1.5 V
C. 2.37 V
D. 1.95 V
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Correct Option
Explanation
The answer key in the OCR indicates 1.85 V; stopping potential is determined from photon energy minus work function divided by e, giving the value shown.
1235
A distant star known to contain Hg that emits its characteristic red colour. On observing the spectrum of this star from the earth, the wavelength is found to have shifted towards higher wavelength side. The star is
A. at rest
B. moving away from the observer on the earth
C. moving towards the observer on the earth
D. the characteristics of the element on the star are different than its characteristics on the earth
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Correct Option
Explanation
A shift to higher wavelengths (redshift) indicates the source is receding, so the star is moving away from the observer.
1236
Which of the following has lower energy quanta?
A. X-ray
B. White light
C. Gamma-ray
D. None of these
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Correct Option
Explanation
Among the listed electromagnetic radiations, visible (white) light photons have much lower energy quanta than X-rays or gamma rays.
1237
The 'X' in X-rays means
A. Xenon
B. explosion
C. X for unknown
D. X makes the spot
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Correct Option
Explanation
The 'X' historically denotes an unknown type of radiation, hence 'X for unknown'.
1238
The phenomenon in which the wavelength of scattered X-rays is larger than the incident X-rays is known as
A. annihilation of matter
B. Compton's effect
C. Zeeman's effect
D. photoelectric effect
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Correct Option
Explanation
Compton scattering increases the wavelength of scattered X-rays compared to incident X-rays.
1239
The apparent wavelength of light from a star moving away from the earth is 0.2% more than its real wavelength. The velocity of the star is
A. 300 km/sec
B. 600 km/sec
C. 1200 km/sec
D. 150 km/sec
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Correct Option
Explanation
Redshift Δλ/λ = v/c = 0.002 → v = 0.002 × 300000 km/s = 600 km/s.
1240
The Wien's displacement law expresses relation between:
A. frequency and temperature
B. wavelength corresponding to maximum energy and temperature
C. temperature and amplitude
D. wavelength and radiating power of black body
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Correct Option
Explanation
Wien's law states that the wavelength of maximum emission is inversely proportional to temperature (λ_max × T = constant).
