Question

Unpolarized light is shines upon a photocell for one hour. Then, two polarizers, whose transmission axes are offset by 60°, are placed in front of the photocell such that the light must first pass through the polarizers before reaching the cell. How much time is required for the photocell to receive the same total energy as it received in one hour’s time without the polarizers present?

Answer 1

let Io is the intensity of unpolarised light.
Intencity of light passing through first polariser, I1 = Io/2

Intensity of light passing through second polairzer, I2 = I1*cos^2(theta)

= (Io/2)*cos^2(60)

= Io/8

Energy obsorbed, E = I*A*t (A ia area and t is the time taken)
when light is transmitted through polarizers the intensity is decreasing to 1/8 times.

energy obsorbed with out polarisers = energy obsorbed with polarisers
Eo = E
Io*A*to = I*A*t
Io*to = (Io/8)*t

==> t = 8*to

= 8 hours <<<<<-----------Answer
so, the time is required for the photocell to receive the same total energy as it received in one hour’s time without the polarizers present = 8 hours <<<<<<<<----Answer