## E=pc Equation

$\lambda=\frac{h}{p}$

SophiaNguyen_2L
Posts: 105
Joined: Wed Sep 30, 2020 9:59 pm

### E=pc Equation

Hello! I'm a little confused about some of the equations Professor Lavelle wrote on his whiteboard during the lecture at minute 38:35. From what I understand, p(momentum)=m(mass)*v(velocity). Below that equation he had on the board, Professor Lavelle wrote "E=pc." I'm confused about this because I thought velocity was doubled here, since velocity is part of the "p" in the equation and "c" itself is the velocity of light. If anybody could clarify/explain this for me, I'd really appreciate it! Thank you in advance!

SamanthaTolentino 3D
Posts: 131
Joined: Wed Sep 30, 2020 10:03 pm

### Re: E=pc Equation

I think when he wrote that equation, he was talking about how light does not have a rest mass but it has momentum therefore, the energy of light = momentum* speed of light.

Jagveer 1I
Posts: 95
Joined: Wed Sep 30, 2020 9:33 pm
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### Re: E=pc Equation

He was just trying to show that from E=mc^2, you could get E=pc since p=mv and v=c as you stated, so E=m*c*c, or E=pc.

Inderpal Singh 2L
Posts: 153
Joined: Wed Sep 30, 2020 10:02 pm
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### Re: E=pc Equation

He was trying to show all the other equations you could derive from E=m*c^2. This is similar to the equations we used in the photoelectric effect and how we would use what is given to us to answer a problem. Depending on what we are given, we can form different types of equations.