# Wavelength-stopping potential dependence

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## Homework Statement

Consider a point source emitting light of wavelength 5000 A. Light from this source is falling on a metallic cathode of photoelectric cell. It is also given that energy of a photon of wavelength 10,000 A is 1.23 eV. If the source of 5000 A is replaced by 2500 A wavelength but emitting same no. of photons in unit time, what will happen to the saturation current and stopping potential respectively?

## Homework Equations

eV=KE(max)
no. of electrons ejected=no. of photons colliding (energy above work function)

## The Attempt at a Solution

since no. of electrons ejected does not change with change in energy of photon, saturation photocurrent remains same.
halving the wavelength doubles the energy of a photon and therefore the electron, since V and energy of electron=0.5mv^2 are directly proportional. Stopping potential should be doubled, but the answer is given as it is more than doubled. Where am I wrong? I suspect doubling wavelength won't double the KE since work function is not zero- but then how do I arrive at the correct relation?
I'd appreciate some help, thank you

## Answers and Replies

mjc123
Science Advisor
Homework Helper
Where did you get your "relevant equation"? Isn't it missing something?

Gold Member
Where did you get your "relevant equation"? Isn't it missing something?
hf=work function+eV

mjc123
Science Advisor
Homework Helper
So if you double hf without changing WF, how will eV change?

Gold Member
So if you double hf without changing WF, how will eV change?
Right, it will more than double

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Thank you very much for your help :D