Question

If intensity of light is doubled then what will be the effect on
i) Kinetic energy of photo electron
ii) Photoelectric current

Answer 1

If both the intensity and the frequency of incident light is doubled then the photocurrent remains roughly the same, while the maximum kinetic energy of photo-electrons increases by more than two times.

Since we are doubling the frequency, the energy of the photo-electron increases. To understand why the kinetic energy increases by more than two times, take a look at the photo-electric equation:

Initially,

K1=hf−ϕK1=hf−ϕ

When we double the frequency from f to 2f,

K2=h(2f)−ϕK2=h(2f)−ϕ

or, K2=2(hf−ϕ)+ϕK2=2(hf−ϕ)+ϕ

So, a double in frequency causes a more than two times increase in Kinetic Energy.

Now, intensity is defined as the amount of power passing through an area of unit area. The overall power of the source of light (intensity) is doubled. Each photon has double the energy as before. So, the number of photons bombarding the metal surface is the same - so the same number of photo-electrons are ejected. The photo-current is a measure of how many electrons are coming out - as the number of electrons is the same, the photo-current remains the same.

hope this helps you
regards nishita