Question

A photo-cell is illuminated by a source of light, which is placed at a distance d from the cell. If the distance become d/2, then number of electrons emited per second will be : -

Answer 1

Solution :

Number of electrons emitted per second is alpha 1/d^2

Hence if d changes to d/2

No of electrons emitted becomes 4 times the original

Answer 2

The number of electron emitted will be i/4 of the original number

Explanation:

Given Data:

Intensity, I =  E /At

E = the total energy of source,

A = area of illuminated surface,

t = time

Solution:

I = E /  4πr^2  t  

I1 / I2 = E /  4πr1^2 t  x  4πr2^2  t  / E

I1 / I2 = r2^2 / r1^2

I1 / I2  = 4 / 1

I2 / I1 = 1 / 4