Number of photons emitted from a laser

[pat666]

Homework Statement

A 35mW laser produces 526nm green light.
What is the number of photons it emits each second?
1.9×10¹⁷
1.9×10¹⁸
1.0×10¹⁷
9.3×10¹⁶

Homework Equations

The Attempt at a Solution

I've been playing with E=hf and lambda = h/p ----- no success!
The textbook I am using doesn't have much on photons/photoelectric effect - nothing that helps me with this question at least. the "photon wavelength-momentum relation" is I think the most relevant to this question?? The textbook doesn't actually say what p is so I assumed number of photons but that's wrong since it doesn't work.

anyway need some help please.

 

[ehild]

Calculate the energy of one photon. You need to get the frequency from the wavelength.

ehild

 

[pat666]

thanks ehild - solved the problem