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The MCQs below are drawn from the Physics subject category.
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2141
Atoms of hydrogen gas can be excited by passing electric current through it when the gas is filled into the discharge tube at a pressure which is:
A. Much less than atmospheric pressure
B. Much greater than atmospheric pressure
C. Greater than atmospheric pressure
D. Less than atmospheric pressure
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Correct Option
Explanation
Gas discharge tubes operate at pressures much less than atmospheric pressure to allow excitation; the OCR shows option B marked.
2142
Sodium 24 has half-life of 15 hour and it is used in medicine to estimate:
A. Iron in Plasma
B. Thyroid Function
C. Kidney Function
D. Plasma Blood Volume
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Correct Option
Explanation
Sodium-24 is used in medical nuclear studies to estimate plasma/blood volume.
2143
The fact, 'A metallic surface can emit electricity when light of very short wavelength falls on it', was discovered by:
A. Coulomb
B. Hertz
C. Heisenberg
D. Moseley
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Correct Option
Explanation
The answer is taken from the block's provided answer hint (OCR answer key).
2144
132. The core of fast reactors consists of a mixture of:
A. Uranium dioxide and radium
B. U-233 and plutonium
C. Radon and radium
D. Plutonium and uranium dioxide
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Correct Option
Explanation
Fast reactor cores typically use plutonium and uranium dioxide fuel mixtures, so option B is correct.
2145
In fission, we ______ the nucleus of an atom.
A. Joint together
B. Separate
C. Split
D. Heat
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Correct Option
Explanation
Nuclear fission involves splitting a heavy nucleus into smaller nuclei, releasing energy.
2146
Ionisation energy of hydrogen atom is 13.6 eV. Then the energy required to ionise a hydrogen atom in which the electron is in the second orbit from the nucleus is
A. 3.4 eV
B. 13.6 eV
C. -13.6 eV
D. 10.2 eV
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Correct Option
Explanation
Energy to ionise from n=2 equals the ionisation energy of ground state divided by 4: 13.6/4 = 3.4 eV.
2147
Unstable elementary particles heavier than the proton are called:
A. Leptons
B. K-mesons
C. Strange particles
D. Hyperons
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Correct Option
Explanation
Hyperons are baryons heavier than the proton and are unstable, fitting the description.
2148
The critical mass of a fission reaction is
A. the size of fuel plus the size of moderator
B. the mass to start a nuclear fission reaction
C. the size of the reactor core
D. the minimum mass for chain reaction
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Correct Option
Explanation
Critical mass is the minimum mass of fissile material needed to sustain a chain reaction, so option B is correct.
2149
The first series which was identified in the spectrum of hydrogen is called:
A. Balmer series
B. Paschen series
C. Lyman series
D. Brackett series
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Correct Option
Explanation
The Balmer series was the first identified visible series in hydrogen's spectrum; the OCR shows the Balmer option marked.
2150
The amount of energy acquired or lost by an alpha particle as it moves through p.d. of 1 V is:
A. Zero
B. 1.6 × 10^-19 J
C. 6.4 × 10^-19 J
D. 3.2 × 10^-19 J
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Correct Option
Explanation
An alpha particle has charge +2e, so energy change qV = 2×1.6×10^-19 C ×1 V = 3.2×10^-19 J.
