Photoelectric Effect: Which Answer is Correct?

1. Jun 10, 2009

science.girl

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

A photon of wavelength 250 nm ejects an electron from a metal. The ejected electron has a de Broglie wavelength of 0.85 nm.

(a) Calculate the kinetic energy of the electron.

2. Relevant equations

KE = .5mv^2

3. The attempt at a solution

ANSWER1: E = .5mv^2 and v = h/m$$\lambda$$
Therefore, E = .5m(h/$$\lambda$$)^2

Substituting values (including $$\lambda$$ = .85*10^(-9)), you get 3.34*10^(-19) J

250e-9=6.63e-34/(2*9.11e-31K)
K=6.87e-4 Joules

2. Jun 10, 2009

diazona

The first one is correct, I think. But the second method will also give you the correct answer if you do it properly - you just made a couple of little mistakes (one algebraic, one plugging in the wrong number).

3. Jun 10, 2009

science.girl

Ah! Thank you very much!