A simple Stop Potential question... I thought

[HawkBear05]

1. The problem statement, all variables and given/known data

What is the cutt off wavelength of the material, and max nrg of electrons when we know the stop potent. of the material is 8 V and the wavelegnth is 100 nm. What is stop potent. of material when wavelegthn is 200 nm?

2. Relevant equations

E = hv - w
where E = hv
and h = planks constant or "h cross"

3. The attempt at a solution
hv = hv - w = E
8 = h (c/wavelegthn) - w
8 = 6.6* 10 ^-34 (3*10^8/100) - w
solved for w... but how do I find cut off nm? and max nrg of electron

at 200 nm...
E = h (c/wavelegthn) - w
E = 6.6* 10 ^-34 (3*10^8 / 200) - 0
solved for E, but I pretty sure its wrong.

[ApexOfDE]

I dont understand your question but from this line E = hv - w, i think your problem is about photoelectronic effect, right?

If yes, then you should read about this article: http://en.wikipedia.org/wiki/Photoelectric_effect .

Maximum kinetic energy of e can be give by K = |eV|.

[HawkBear05]

thanks for the link