Question

in photoelectric effect ,, why is
maximum KE = eV ????
where V is the stopping potential

Answer 1

why do you think?

Answer 2

try to solve for the work function

Answer 3

obvious, isnt it? it uses chapter 2 knowledge.

Answer 4

If you have a uniform E field between points A and B, having potential difference V, and take an electron and let go at A,

then by the time it reaches B, the field would have done work =eV right? This manifests itself as kinetic energy =

0.5mv^2(the electrons pot. energy got converted to k.e)

Now do the reverse.. Imagine an electron already coming in with k.e at point A, to stop it by the time it reaches point B,

you need to put exactly the same field (in opp direction, but thats a detail) with same potential difference calculated as

eV = 0.5mv^2 (such that when it reaches point B, all the k.e gets converted to p.e). and this BY definition is what we

call as stopping potential
if you put Less, then electron won't stop at B, (some residual K.E is present), if you put higher V, then it stops even before it reaches point B.