## E = pc

Hannah Lee 2F
Posts: 99
Joined: Thu Jul 11, 2019 12:15 am

### E = pc

When would we have to use the E = pc equation that is listed in the equations sheet and mentioned briefly in our notes? Can someone clarify for me in what problems/situations feature this equation? I don't think I've ever encountered it before in the homework.

Caitlyn Tran 2E
Posts: 85
Joined: Fri Aug 09, 2019 12:15 am

### Re: E = pc

E=pc is just an equation that relates momentum with energy. We used it in our notes to show how when used in conjunction with E=hv (which relates energy to frequency), we can derive De Broglie's wave equation. I think that we would only use E=pc in a problem if we were given the velocity of an electron and expected to find energy or vice versa.

TarynD_1I
Posts: 85
Joined: Sat Aug 24, 2019 12:17 am

### Re: E = pc

I think that you use E = pc when mass is not considered (maybe like a photon, because Lavelle said in class that photons do not have mass, but they have momentum).

005206171
Posts: 85
Joined: Wed Sep 18, 2019 12:20 am

### Re: E = pc

E=pc is especially helpful to find the momentum of light which does not have rest mass (so you can't use p=mv). Light has no rest mass but does have momentum in the form of energy.