Assertion (A): Photo cell is also called electric eye.
Reason (R): Photo cell can see the things placed in front of it.
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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A photocell is indeed commonly referred to as an 'electric eye' due to its light-sensing ability. So, (A) is true. However, a photocell merely detects the presence or intensity of light; it does not 'see' or form images of objects in front of it in the way a biological eye does. Therefore, (R) is false.
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): 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.
Assertion (A): Output frequency of time varying DC voltage in a full wave rectifier is twice of input frequency.
Reason (R): A center tap transformer increases the frequency of input.
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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A full-wave rectifier converts both halves of an AC input into a pulsating DC output, effectively doubling the input frequency. Thus, Assertion (A) is true. A transformer only steps up or steps down voltage and current; it does not alter the frequency of the AC signal. Hence, Reason (R) is false.
Assertion (A): Light emitting diode (LED) emits self radiation.
Reason (R): LED are reverse biased p-n junctions.
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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Concept: LED operation.
LEDs are \(p-n\) junctions that emit light when forward biased due to electron-hole recombination. Reverse biasing does not cause light emission. Thus, Assertion (A) is true, but Reason (R) is false.