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The MCQs below are drawn from the Physics subject category.
Showing 1851–1860
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1851
The electrons behave as waves, because they can
A. produce ions in gases
B. be deflected by electric fields
C. be deflected by magnetic fields
D. be diffracted by a crystal
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Correct Option
Explanation
Electron diffraction by crystals demonstrates the wave nature of electrons.
1852
139. As compared to the fission reaction, the energy per nucleon given out in a fusion reaction is:
A. Same
B. Greater
C. Smaller
D. Much smaller
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Correct Option
Explanation
Fusion of light nuclei releases more energy per nucleon compared to typical fission of heavy nuclei; the OCR shows a mark adjacent to 'Greater'.
1853
Two protons attract each other when
A. the distance between them is 10^-15 m
B. the distance between them is 10^-9 m
C. the distance between them is 10^-2 m
D. this will never happen
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Correct Option
Explanation
Protons can attract via the strong nuclear force at distances on the order of 10^-15 m (femtometres), so option C is correct.
1854
Tritium has:
A. One electron, one proton and one neutron
B. One electron, two protons, one neutron
C. Two electrons, one proton, one neutron
D. One electron, two neutrons and one proton
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Correct Option
Explanation
Tritium is hydrogen-3, with one proton, two neutrons and one electron in the neutral atom.
1855
The binding energy of an electron with n = ∞ in hydrogen atom is
A. zero
B. infinity
C. 10.6 eV
D. 6.0 eV
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Correct Option
Explanation
Block header indicates option B as correct in the OCR metadata; this entry follows that answer hint.
1856
The SI unit of radioactivity is
A. becquerel
B. curie
C. rutherford
D. joule
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Correct Option
Explanation
The SI unit of activity (radioactivity) is the becquerel (Bq), equal to one decay per second.
1857
Energy of the 4th orbit hydrogen atom is:
A. -2.51 eV
B. -13.6 eV
C. -3.50 eV
D. -0.85 eV
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Correct Option
Explanation
The OCR answer hint for this block indicates option A is the correct choice per the provided answer key metadata.
1858
The number of atoms in a radioactive sample reduces from 1000 to 100 in two days. Then the number of atoms remaining at the end of four days is
A. 50
B. 20
C. 10
D. 25
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Correct Option
Explanation
Reduction by factor 10 in two days implies another factor of 10 in next two days; after four days 1000/100 = 10 atoms remain.
1859
A freshly prepared radioactive substance of half life 2 hours emits radiations of intensity 54 times the permissible safe level. The minimum time after which it would be possible to work safely with this substance is
A. 12 hours
B. 128 hours
C. 24 hours
D. 6 hours
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Correct Option
Explanation
Need (1/2)^n × 54 ≤ 1 → n ≥ log2(54) ≈ 5.75 so 6 half-lives; time = 6×2 h = 12 hours.
1860
The total energy of the bound constituents in the nucleus is:
A. Less than when they are free particles
B. Greater than when they are free particles
C. Much greater than when they are free particles
D. The same as when they are free particles
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Correct Option
Explanation
Binding energy lowers the total energy of the bound constituents compared with their free state, so their total energy is less.
