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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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): Electron hole recombination takes place in P-region and N-region of PN Junction diode except in depletion region.
Reason (R): Electric field in depletion region oppose the diffusion.
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
View Answer
Assertion (A) is generally true in simplified models, where most recombination occurs in the quasi-neutral P and N regions. While some recombination does occur in the depletion region, its contribution to the overall current is often considered secondary for typical forward-biased diodes.
Reason (R) is true; the electric field in the depletion region acts as a barrier, opposing the diffusion of majority carriers across the junction. (R) does not explain the spatial distribution of recombination described in (A).
Assertion (A): In an OR gate if any of the input is high the output is high.
Reason (R): OR gate is the basic gate.
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
View Answer
Assertion (A) is the fundamental definition of an OR gate, which is true. Reason (R) is also true as an OR gate is a basic logic gate. However, (R) does not explain the functional behavior of the OR gate described in (A).
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
View Answer
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): A NAND gate can be obtained by using NOR gates.
Reason (R): NOR, NAND and XOR gates are called universal gates.
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
View Answer
NAND and NOR gates are universal gates, meaning any other logic gate (including NAND) can be constructed using only NOR gates. Hence, Assertion (A) is true. However, while NAND and NOR are universal gates, XOR is not. Therefore, Reason (R) is false.
Assertion (A): Width of depletion region is reduced in forward bias.
Reason (R): In n-type semiconductor majority charge carriers are free electrons while in p-type they are holes.
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
View Answer
When a p-n junction is forward biased, the applied voltage counteracts the internal electric field, causing majority carriers to move towards the junction and reducing the depletion region's width. Thus, Assertion (A) is true.
Reason (R) correctly states the majority carriers in n-type (electrons) and p-type (holes) semiconductors, which is also true. However, Reason (R) does not explain why the depletion region width reduces under forward bias. Hence, both are true, but R is not the correct explanation for A.