1.

Assertion: A p-n junction with reverse biase can be used as a photo-diode to measure light intensity. Reason: In reverse bias condition the current is small but it is more sensitive to change in incident light intensity.

Answer»

If both the assertion and reason are true and reason is a true explantion of the assertion.
If both the assertion and reason are true but THEREASON is not true the correct explantion of the assertion.
If the assertion is true but reason false
If both the assertion and reason are false.

Solution :Photo-diode is a reverse biased `p-n` junction diode as shown in figure. At the `p-n` junction there exists a junction field which at equilibrium, does not permit the flow of charge carriers across the junction.

When such a `p-n` diode is illuminated with light photons having ENERGY `hvgtE_(g)` and intensities `I_(1).I_(2),I_(3)` ETC., the electron and hole pairs generated in the depletion layer (or near the junction) will be across the junction. There would be a change in the reverse SATURATION current as shown in figure. Hence, a measurement of the change in the reverse saturationcurrent as shown in figure current on illumination can give the values of the light INTENSITY.

Hence, option (a) is true.


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