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The MCQs below are drawn from the Physics subject category.
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2241
With increase of temperature, the Fermi energy level in n-type semiconductors
A. Remains unchanged
B. Oscillates
C. Moves towards conduction band
D. Moves towards valence bands
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Correct Option
Explanation
In n-type semiconductors increasing temperature increases intrinsic carriers and shifts the Fermi level closer to the conduction band.
2242
Compton's effect was presented by
A. J.J. Thomson
B. Compton
C. Neil Bohr
D. Mosely
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Correct Option
Explanation
The Compton effect was presented by Arthur H. Compton, corresponding to option D.
2243
A nucleus with an excess of neutrons may decay radioactively with the emission of:
A. A neutron
B. An electron
C. A positron
D. A proton
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Correct Option
Explanation
The OCR answer key lists option A for this question in the answer listing provided for question 100.
2244
The mass of a helium nucleus is equal to
A. 5.0015 u
B. 4.0015 u
C. 3.0015 u
D. 2.0015 u
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Correct Option
Explanation
A helium nucleus (alpha particle) has mass approximately 4.0015 atomic mass units.
2245
Which of the following decay modes are known for Σ° hyperon?
A. Σ° -> π+ + Λ
B. Σ° -> Λ + γ
C. Σ' -> π' + Λ
D. Σ° -> P + c- + Λ
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Correct Option
Explanation
Σ° decays electromagnetically to Λ plus a photon (γ), which is the established decay mode (option A).
2246
Which of the following is used to estimate the circulation of blood in a patient?
A. Carbon-14
B. Carbon-12
C. Phosphorus-32
D. Sodium-24
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Correct Option
Explanation
Radioactive sodium-24 has been used as a tracer to study blood circulation due to its biological behavior and detection properties.
2247
Which among the following is a positively charged particle emitted by a radioactive element?
A. Gamma rays
B. Alpha rays
C. Beta rays
D. Cathode rays
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Correct Option
Explanation
Alpha particles are positively charged helium nuclei emitted in some radioactive decays, whereas beta particles are electrons (negative) and gamma rays are neutral.
2248
The average energy released per fission of U235 is about
A. 200 MeV
B. 2 keV
C. 200 eV
D. 2 MeV
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Correct Option
Explanation
A typical fission of U-235 releases on the order of 200 MeV of energy, so 200 MeV is correct.
2249
The rest masses of both K1 and K2 mesons is equal to:
A. 973 m.
B. 974 m.
C. 972 m.
D. 971 m.
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Correct Option
Explanation
The block's answer hint indicates option A (974 m.) as the rest mass value given in the OCR text.
2250
An electron in n = 1 orbit of hydrogen atom is bound by 13.6 eV. If a hydrogen atom is in the n = 3 state, how much energy is required to ionise it?
A. 3.4 eV
B. 4.53 eV
C. 1.51 eV
D. 13.6 eV
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Correct Option
Explanation
Ionisation energy from level n is 13.6 / n^2 eV; for n = 3 this is 13.6/9 ≈ 1.51 eV, so option D is correct.
