(adsbygoogle = window.adsbygoogle || []).push({}); HELP!!! photoelectric effect

Ok guys got a question on quantum physics - photoelectric effect i wanna run past you before i attempt a solution.

The question is as follows;

In a photoelectric-effect experiment, light of wavelength 420nm is incident on a sample of sodium. The work function of sodium is 3.67*10-19 J.

Calculate the stopping potential required to stop all electrons from reaching the anode.

Ok so im planig to use einsteins photoelectric equation of 1/2 m_{e}v^{2}= hf-psi(as in work function)

Im guessing i need to convert the wavelength to frequency so have come up with the solution 7.137915667e^{11}

so this in the equation gives me 6.63*10^{-34}* 7.14285713*10^{14}- 3.67*10-19 J = n = -3.665267562

So this is the result of the maximum kinetic energy E of the electrons.

I am a bit worried as my result is a minus!!!!!!!! which i imagine is impossible

after that i believe i am to work out the potential differnence to stop the electrons.

That i am a bit unclear on how to do so any help would be much appreiciated :)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: HELP photoelectric effect

**Physics Forums | Science Articles, Homework Help, Discussion**