Assertion (A): The number of electrons in n-type semiconductor is higher than the number of electrons in a pure silicon semiconductor.
Reason (R): The law of mass action is applicable only to n-type semiconductors.
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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In n-type semiconductors, donor impurities increase the number of free electrons, making Assertion (A) true. The law of mass action (\(n_e n_h = n_i^2\)) is a fundamental principle applicable to all types of semiconductors (intrinsic, n-type, p-type), so Reason (R) is false.
Assertion (A): The conductivity of an intrinsic semiconductor depends on its temperature.
Reason (R): No important electronic device can be developed using intrinsic semi conductor.
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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In an intrinsic semiconductor, conductivity increases with temperature due to increased generation of electron-hole pairs. So Assertion (A) is true. Intrinsic semiconductors have limited practical use due to low conductivity, making Reason (R) true in terms of 'important' devices. However, (R) does not explain (A).
Assertion (A): Width of depletion region is reduced in forward bias.
Reason (R): In forward bias external battery reduced the internal electric field in depletion layer.
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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In forward bias, the external voltage opposes the built-in potential barrier, effectively reducing the internal electric field across the depletion region. This reduction in the electric field causes the depletion region to narrow. Hence, both Assertion (A) and Reason (R) are true, and (R) correctly explains (A).
Assertion (A): Bridge full wave rectifier is more used than centre tap full wave rectifier.
Reason (R): In bridge full wave rectifier four diodes are used.
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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Bridge full-wave rectifiers are more popular because they do not require a costly center-tapped transformer and offer higher output voltage. So Assertion (A) is true. Reason (R) is also true as a bridge rectifier uses four diodes. However, the number of diodes is not the primary reason for its preference over a center-tap rectifier.
Assertion (A): The semiconductor used for fabrication of visible LED must at least have a band gap of 1.8 eV.
Reason (R): The spectral range of visible light is from 0.4 eV to 1.8 eV.
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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For visible light emission, the photon energy must be within the visible spectrum, which corresponds to energies from approximately \(1.8\) to \(3.1 \text{ eV}\). Thus, Assertion (A) is true. Reason (R) states the range from \(0.4\) to \(1.8 \text{ eV}\), which is incorrect for visible light.
Assertion (A): In an oscillator, the feedback is in the same phase which is called as positive feedback.
Reason (R): If the feedback voltage is in opposite phase the gain is greater than one.
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; for sustained oscillations, positive feedback (in-phase) is required. Reason (R) is false; opposite phase feedback, known as negative feedback, typically reduces the amplifier's gain, not increases it.
Assertion (A): Working principle of photodiode and photocell is same.
Reason (R): Biasing circuit for photodiode and photocell is same.
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 false; photodiodes rely on \(p-n\) junction semiconductor physics, while photocells (e.g., photoemissive cells) often rely on the photoelectric effect. Reason (R) is also false as their biasing circuits differ significantly (e.g., photodiode often reverse biased, photocell can be forward biased or unbiased).
Assertion (A): GaAs is preferred for making solar panels.
Reason (R): \(\Delta E_g\) for GaAs is \(1.5\text{ eV}\), and sun’s radiation has highest intensity around this energy level.
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 terms of performance; GaAs solar cells offer very high efficiency. Reason (R) is also true; the bandgap of GaAs (approx. \(1.42\text{ eV}\,) is near \(1.5\text{ eV}\), which matches well with the peak intensity of the solar spectrum. (R) correctly explains (A) as this optimal bandgap is key to its high efficiency.
Assertion (A): In LED \(e^-\)-hole pair recombination gives us photon.
Reason (R): In LED \(e^-\)-hole pair recombination occurs in depletion region.
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; LEDs emit photons when electrons and holes recombine. Reason (R) is false; while carriers cross the depletion region, significant recombination leading to light emission primarily occurs in the quasi-neutral regions (or active layer) under forward bias, not mainly within the depletion region itself.
Assertion (A): In a N-type semiconductor, the number of holes get reduced.
Reason (R): Rate of recombination of holes would increase due to the increase in the number of electrons
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 an N-type semiconductor, donor doping increases electron concentration, which, by mass action law (\(np=n_i^2\)), reduces the equilibrium hole concentration. Reason (R) is true; the increased number of electrons in an N-type semiconductor leads to a higher rate of recombination with the minority holes. (R) correctly explains (A) as this increased recombination helps establish and maintain the lower equilibrium hole concentration.