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
View Answer
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).
Boolean expression for the truth table given below is (A and B are inputs and Y is output)
\[\begin{array}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 1 \\ \hline 0 & 1 & 0 \\ \hline 1 & 0 & 0 \\ \hline 1 & 1 & 0 \\ \hline \end{array}\]
1. \(\overline{A} + \overline{B}\)
2. \(\overline{A} \cdot \overline{B}\)
3. \(A + B\)
4. \(A \cdot B\)
View Answer
The output \(Y\) is high only when both inputs \(A\) and \(B\) are low. This corresponds to a NOR gate, represented by the expression \(Y = \overline{A+B} = \overline{A} \cdot \overline{B}\).
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.