Hey guys, I was just wondering, I was given a certain frequency of light, and I was asked to calculate the momentum of the photon. Do I use plancks constant in joules or eV? How do you know when to use eV or J in other cases?

I would actually suggest using de Broglie wavelength equation to find the

*momentum* of a photon. Planck's equation is usually used to find the energy of a photon. (In the end it is really ur choice though ).

Anyway to answer your question:

The energy of a photon is in joules. If you are going to use planck's equation it would possibly be in joules. Hope that answered ur question.

P.S. In case u were wondering what is de brogile wavelength equation :

p = h / lambda

where h is planck's constant and lambda is wavelength of the certain frequency of light ( u can find wavelength of light through frequency as speed of light = wavelength * frequency