# Quantum Theory - The Photo-Electric Effect

Hi, I got this question and I have spent a while trying to crack it but I'm still stuck.

White light, with frequencies ranging from 4.00 x10^14 Hz to 7.85x10^14 Hz, is incident on a potassium surface. Given that the work function of potassium is 2.24 eV, find the following values.
(a) the maximum kinetic energy of electrons ejected from this surface
eV
(b) the range of frequencies for which no electrons are ejected
minimum -
maximum -

For part a) I used the formula e=hv, as described by Planck. For Planck's Constant h I used a value of 6.62x10^-34 and for my frequency v I used the highest value in the range i.e. 7.85x10^14 in order to yield the highest K.E. but I came up with an answer of 5.205x10^-19 which is wrong...can someone point me in the right direction? Thanks.