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The MCQs below are drawn from the Physics subject category.
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1831
Use the nuclear shell model to determine the ground state spin of 57 Zn:
A. 5/2
B. 1/2
D. 3/2
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Explanation
57Zn has an odd neutron (N = 27); in the shell model the unpaired neutron is expected to occupy an f5/2-type orbital, giving a ground-state spin of 5/2.
1832
Radioactivity is the phenomenon associated with
A. Production of radio waves
B. Decay of nucleus
C. Reception of radio waves
D. Transmission of radio waves
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Explanation
Radioactivity refers to spontaneous decay of unstable atomic nuclei, not electromagnetic radio wave processes.
1833
If 20% of the radioactive material decays in one week, then the amount of the material left after 2 weeks is equal to
A. 60%
B. 75%
C. 64%
D. 55%
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Explanation
If 20% decays in one week, 80% remains; after two weeks remaining = 0.8×0.8 = 0.64 = 64%.
1834
If D is the absorbed dose, D_e is equivalent dose, then the relation between them is:
A. D = D_e × RBE
B. RBE = D × D_e
C. Any of these
D. D_e = D × RBE
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Explanation
Equivalent dose (D_e) is defined as absorbed dose (D) multiplied by the radiation weighting factor (RBE), so D_e = D × RBE.
1835
According to Einstein's photoelectric equation, the plot of the kinetic energy of the emitted photoelectrons from a metal vs the frequency of the incident radiation gives a straight line whose slope
A. Depends on the nature of the metal used
B. Depends on the intensity of the radiation
C. Is the same for all metals and independent of the intensity of the radiation
D. Depends both on the intensity of the radiation and metal used
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Explanation
The slope of kinetic energy vs frequency is Planck's constant h, which is universal and does not depend on the metal or the intensity.
1836
After a time equal to four half-lives the amount of radioactive material remaining undecayed is
A. 50%
B. 25 %
C. 12.50%
D. 6.25%
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Correct Option
Explanation
After four half-lives remaining fraction = (1/2)^4 = 1/16 = 6.25%, so option A is correct.
1837
Which of the following transitions in a hydrogen atom emits photon of the highest frequency ?
A. n = 2 to n = 6
B. n = 2 to n = 1
C. n = 1 to n = 2
D. n = 6 to n = 2
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Explanation
Among the listed emissions, transition n=2→1 has the largest energy difference and thus the highest frequency.
1838
When an electron beam is incident on a metal target, then the intensity of X-rays produced depends on which property of incident electrons
A. wavelength
B. energy
C. number of electrons
D. velocity
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Explanation
X-ray intensity is proportional to the number of incident electrons (tube current); more electrons produce higher intensity.
1839
On which factor cut-off wavelength of X-ray coming from a Coolidge tube depends upon?
A. Accelerating voltage
B. Target material
C. Filament temperature
D. Separation between target and the filament
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Explanation
The cut-off (minimum) wavelength is determined by the accelerating voltage; higher voltage yields shorter minimum wavelength.
1840
Matter waves
A. can be diffracted
B. are longitudinal waves
C. travel with the speed of light
D. are electromagnetic in nature
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Explanation
Matter waves (de Broglie waves) can exhibit diffraction, demonstrating their wave-like properties.
