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.
Assertion (A): Avalanche breakdown dominates when the doping concentration is high and depletion layer is thin.
Reason (R): Zener breakdown occurs due to the collision of minority charge carrier.
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
Concept: \(p-n\) junction breakdown.
Avalanche breakdown occurs in lightly doped junctions with wider depletion regions. Zener breakdown occurs in heavily doped junctions due to quantum tunneling, not minority carrier collisions. Thus, both (A) and (R) are false.
Assertion (A): The logic gate NOT can not be built using diode.
Reason (R): The output voltage and the input voltage of the diode does not have \(180^{\circ}\) phase difference.
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 because a NOT gate requires active components to provide inversion and gain, which a passive diode cannot do. Reason (R) is true because a diode circuit does not inherently provide the \(180^{\circ}\) phase shift characteristic of logic inversion. Thus, (R) correctly explains (A).
In a reverse biased diode when the applied voltage changes by \(5 \text{V}\), the current is found to change by \(2 \mu\text{A}\). The reverse bias resistance of the diode is:
1. \(10^6 \Omega\)
2. \(2 \times 10^6 \Omega\)
3. \(5 \times 10^6 \Omega\)
4. \(2.5 \times 10^6 \Omega\)
View Answer
Reverse resistance is given by \(R = \frac{\Delta V}{\Delta I}\). Substituting the values, \(R = \frac{5 \text{V}}{2 \times 10^{-6} \text{A}} = 2.5 \times 10^6 \Omega\).
In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R)
Assertion (A): The photo-diode can be used as a photodetector to detect optical signals.
Reason (R): It is easier to observe the change in the current with change in the light intensity, if a forward bias is applied to photodiode.
1. If both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. If both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. If (A) is true statement but (R) is false
4. If both (A) & (R) are false statements
View Answer
Photo-diodes are operated in reverse bias because the fractional change in reverse current upon illumination is far larger and more easily measured than in forward bias.