My chemistry book is covering some basics of energy and photons. I worked most of the problems, but I couldn't figure this one out:

 

If the laser emits [math](1.3)(10^{-19}) J[/math] of energy during a pulse, how many photons are emitted during the pulse?

My chemistry book is covering some basics of energy and photons. I worked most of the problems, but I couldn't figure this one out:

 

You have the wavelength or frequency? That will tell you the energy per photon. [math]E = h\nu = hc/\lambda[/math]

[math](4.69)(10^{14}s^{-1})[/math]

 

I believe that's the frequency.

 

I'm not too sure what variables I'm suppose to be using.

I know the answer is [math](4.2)(10^{16})[/math], but I don't see how.

h = 6.63 x 10^-34 J-s

 

That gives 3.1 x 10^-19 J per photon, which is less than the pulse energy, so something is very wrong.

 

Using your answer, the pulse energy should be 1.3 x 10^-3 J. Typo, or transcription error perhaps?

Probably. What I'm reading seems to be illogical. It seems as if the author uses improper pronoun-antecedent usage.