[eq123]

i've been trying to figure out this problem..

The longest wavelength of light that causes electrons to be ejected from the surface of a copper plate is 243 nm. What is the maximum velocity of the electrons ejected when light of wavelength 200. nm shines on a copper plate?

the answer is 6.22 × 10^5 m/s

any ideas?

[Borek]

You have asked the same question at physicalforums and you were already given several hints - have you tried to use them?

[MrTeo]

You have asked the same question at physicalforums and you were already given several hints - have you tried to use them?

Spotted! 

[eq123]

thank you for nothing!

[sjb]

What equations do you know that may be relevant (perhaps look for Photoelectric effect, or similar)

[Prof. Bohr]

you could work that out using De Broglie's postulate - All matter has an associated wavelength, and the wavelength is inversely proportional to the mass x velocity.
in brief, Lambda = (Planks const)/(mass x veloc.)

Wiki it.

[opti384]

 I think this problem is related to the photoelectric effect.

"The longest wavelength of light that causes electrons to be ejected from the surface of a copper plate is 243 nm. What is the maximum velocity of the electrons ejected when light of wavelength 200. nm shines on a copper plate?"

Here the wavelength of 243nm indicates the minimum frequency of light required for the electrons to be emitted from copper plate. frequency = the speed of light/wavelength. Energy = Plank constant x frequency

Therefore, the maximum KE = the energy of the 200nm wave - work function(which equals to the energy of 243 nm wave).

From the maximum KE, you can determine the velocity.