Photo electri question longest wave length

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Homework Statement

In a photoelectricc experiment,electrons are emitted from a surface illuminated by light of wavelength of 4000*(10^-10), and the stopping potential for these electron is found to be 0.5V. what is the longest wavelength of light that can illuminate this surface and still produce photoelectric current.

Homework Equations

not sure

The Attempt at a Solution

i need help to start the question because i have to clue how to start it... so could someine give me a hint on how to start it..NOT ASKING FOR ANSWER

 

[NobodySpecial]

How much energy does a photon of that wavelength have.
How much energy does an electron lose going through 0.5V
= the energy the photon had left after being emitted

From this you can work out how much energy it took to emit it

 

[Sourabh N]

http://en.wikipedia.org/wiki/Photoelectric_effect#Mathematical_description

Are you familiar with the equations written there?
If yes, simply convert frequency to wavelength (with constants multiplying it, of course) and realize that your stopping potential is their work function. If you do this properly, you will be able to 'see' how to find the longest wavelength.

If not, I'd recommend reading the article from start, or pick up any entry level book in Modern Physics (or maybe University Physics?).

 

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i have seen some but not all... I am trying to work it out now

 

[Brown Arrow]

i see got it. thanks Sourabh N

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