Which opto-electronic device shows the inverse variation in resistance with the incident intensity of light ?

Which opto-electronic device shows the inverse variation in resistance with the incident intensity of light ?

Options:

a. Photo-conductive Cell
b. Photo-transistor
c. Photodarlington
d. Photo-voltaic Cell

Correct Answer:a. Photo-conductive Cell

Explanation:

Photo-conductive Cell is a semiconductor device whose resistance is inversely proportional to intensity of light that falls on it.

Hence, it is also known as 'Photo-resistive Cell' since it works according to the phenomenon of photo-resistivity.

Conceptually, the resistivity of any semiconductor device is dependent on the number of free charge carriers present in it.

In the absence of illumination or light, the number of charge carriers are extremely less and resistivity is tremendously high.

On the contrary, the photons strikes the semiconductor in presence of light and then eventually transfer energy to it.

If the energy of photon exceeds the energy band gap of semiconductor, then liberation of free mobile charge carriers takes place which is also another reason in reducing the value of resistivity.