# Homework Help: Find max kinetic energy

1. Dec 19, 2013

### utkarshakash

1. The problem statement, all variables and given/known data
The electric field associated with a monochromatic beam becomes zero 1.2*10^15 times per second. Find the max kinetic energy of the photoelectrons when this light falls on a metal surface whose work function is 2.0 eV.

2. Relevant equations

3. The attempt at a solution
K(max)=hv-W where W=work function.
I have to find frequency from the given information which I don't know. But I guess it should be 1.2*10^15. Not sure about that.

2. Dec 19, 2013

### Zondrina

I believe your interpretation that $f = 1.2 \times 10^{15} Hz$ would be the case.

Convert your work function into Joules before you use it.

Your equation also seems to be a bit off, it should read:

$E_k = hf - W$

3. Dec 19, 2013

### nasu

Think about a sine function (or even better draw it).
How many times does it go through zero in a period?
It is easier to see if you take a period from a maximum to the next maximum in the sine wave.

4. Dec 19, 2013

### utkarshakash

I got that. Thanks!

5. Dec 19, 2013

### nasu

Then what is the frequency of the light, in the problem?
Or you solved the question already?

6. Dec 20, 2013

### utkarshakash

I solved that.