Assertion (A): Beryllium can be used as a moderator in nuclear fission reactor.
Reason (R): A fast moving electron on collision with a light stationary particle loses most of its energy in nuclear reactor.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; Beryllium is a suitable moderator due to low mass and absorption.
Reason (R) is false; moderation involves neutrons, not electrons. Electrons are not used for moderating neutrons in nuclear reactors. Thus, (A) is true, but (R) is false.
Assertion (A): Nuclear force is short range while gravitation and electric force are universal.
Reason (R): Nuclear force does not follow inverse square law.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; nuclear force is short-range, while gravitational and electric forces are long-range.
Reason (R) is true; nuclear force has a complex dependence, not \(1/r^2\). (R) correctly explains (A) as the absence of inverse square law behavior is characteristic of short-range forces.
Assertion (A): In solid each electron will have a different energy level.
Reason (R): In solid crystal each electron has a unique position and no two electrons see exactly the same pattern of surrounding charges.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Due to the Pauli exclusion principle, no two electrons can occupy the same quantum state. In a solid, each electron experiences a unique electrostatic environment. Thus, Assertion (A) is true, and Reason (R) provides the correct explanation for it.
Assertion (A): As we increase applied voltage on LED intensity of emitted light first increases then decreases.
Reason (R): We use LED in forward bias.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true in a nuanced sense; while intensity generally increases with voltage/current, at very high currents, efficiency can decrease due to thermal effects or Auger recombination (LED droop), leading to a peak and subsequent decrease in intensity. Reason (R) is true; LEDs are operated in forward bias. However, (R) does not explain the intensity variation described in (A).