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The MCQs below are drawn from the Physics subject category.
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2061
A slow neutron can cause fission in
A. thorium-232
B. hydrogen-1
C. uranium-238
D. uranium-235
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Correct Option
Explanation
Uranium-235 readily undergoes fission with slow (thermal) neutrons, so uranium-235 is correct.
2062
Carbon-14 releases:
A. Beta radiation
B. Protons
C. Alpha radiation
D. Neutrons
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Correct Option
Explanation
Carbon-14 is a beta-emitter; it decays by beta radiation (beta-minus decay).
2063
Which of the following can not cause fission in a heavy nucleus?
A. deuteron
B. laser rays
C. proton
D. alpha particle
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Correct Option
Explanation
Charged particles like alphas, protons or deuterons can induce reactions; ordinary laser rays cannot induce nuclear fission, so D is correct.
2064
Which of the following is NOT needed in a nuclear fission reactor?
A. moderator
B. fuel
C. coolant
D. accelerator
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Correct Option
Explanation
A conventional nuclear fission reactor requires fuel, a moderator and a coolant; an accelerator is not required for standard reactors.
2065
At what speed the mass of a body will be doubled?
A. 0.97 c
B. 0.67 c
C. 0.87 c
D. 0.77 c
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Correct Option
Explanation
Relativistic factor γ = 2 gives v = c·√(1 - 1/γ^2) = c·√(3)/2 ≈ 0.866c, i.e. ≈0.87c (option C).
2066
The relation between work function and maximum energy of photoelectrons was discovered by
A. Max. Planck
B. Einstein
C. Stefan
D. Marley
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Correct Option
Explanation
Albert Einstein formulated the photoelectric equation relating work function to the maximum kinetic energy of photoelectrons.
2067
The radius of nth orbit of H-atom can be determined by using the formula
A. r_n = h^2 / 4π^2 k m^2 e^2
B. r_n = n^2 / 4π^2 k m e^2
C. r_n = n^2 h^2 / 4π^2 k m e^2
D. r_n = n h / 4π^2 k m e^2
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Correct Option
Explanation
Bohr radius formula generalizes to r_n ∝ n^2 h^2 divided by constants, matching option A.
2068
Two nuclei are said to be isotones if
A. number of protons possessed by each is the same
B. number of neutrons in one equals the number of protons in the other and vice versa
C. number of neutrons possessed by each is the same
D. number of nucleons possessed by each is the same
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Correct Option
Explanation
Isotones are nuclei that have the same number of neutrons, so option B is correct.
2069
The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectrons emission from this substance is approximately
A. 540 nm
B. 220 mm
C. 400 nm
D. 310 nm
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Correct Option
Explanation
Threshold wavelength λ = hc/φ ≈ 1240 eV·nm / 4.0 eV ≈ 310 nm, so option C is correct.
2070
The nuclei of an element having the same charge number but different mass numbers are called:
A. Isotopes
B. Isomers
C. Isobaric
D. Isobars
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Correct Option
Explanation
Nuclei with the same charge number (same Z) but different mass numbers (different A) are isotopes.
