Question

Given below are two statements ; one is labelled as Assertion $A$ and the other is labelled as Reason $R$

Assertion A: Photodiodes are used in forward bias usually for measuring the light intensity

Reason R: For a p-n junction diode at applied voltage $V$ the current in the forward bias is more than the current in the reverse bias for $\left|V_2\right|>\pm V \geq\left|V_0\right|$ where $V_0$ is the threshold voltage and $V _2$ is the breakdown voltage

In the light of the above statements, choose the correct answer from the options given below

• A. A is true but $R$ is false
• B. A is false but $R$ is true
• C. Both $A$ and $R$ are true but $R$ is NOT the correct explanation $A$
• D. Both $A$ and $R$ are true and $R$ is correct explanation $A$

Answer 1

The Correct Option is B

1. Analyzing Assertion A:
Photodiodes are not used in forward bias for light intensity measurements. Instead, they are used in reverse bias to ensure that the photocurrent is proportional to the incident light intensity.
Hence, Assertion A is false.
2. Analyzing Reason R:
The given statement about the current in a p-n junction diode in forward bias being greater than in reverse bias is correct. The reverse bias current is minimal (leakage current) until breakdown voltage \(V_z\) is reached.
Hence, Reason R is true.
Thus, the correct answer is A is false but R is true. Photodiodes operate in reverse bias mode because the reverse current is directly proportional to light intensity, providing accurate measurement. Forward bias operation is unsuitable for this purpose.