## Comparing E=pc and E=.5mv^2

Tasnia Haider 1E
Posts: 55
Joined: Sat Jul 22, 2017 3:01 am

### Comparing E=pc and E=.5mv^2

When finding the velocity of an electron, which formula should you use, E=pc or E=.5mv^2? Does it depend on if the electron is being described as a particle or a wavelength?

Samantha Joseph 1F
Posts: 48
Joined: Fri Sep 29, 2017 7:04 am
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### Re: Comparing E=pc and E=.5mv^2

It's best to use E = (1/2)mv^2 because you're given the mass m of an electron and you can just solve for v. Also, it doesn't matter what the electron is being described as since the equations you use depend on the information provided to you.

Bansi Amin 1D
Posts: 51
Joined: Fri Sep 29, 2017 7:05 am
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### Re: Comparing E=pc and E=.5mv^2

What information must be provided to determine which equation to use? Is it that E=pc can only be applied to a massless particle because the speed of light is for a massless particle/photon?

Eli Aminpour 2K
Posts: 50
Joined: Fri Sep 29, 2017 7:04 am

### Re: Comparing E=pc and E=.5mv^2

E=0.5mv^2 is the generic physics equation for kinetic energy. It really depends on what variables you are already given when you decide which formula to use. When discussing the photoelectric effect, it is more common to use the Kinetic energy equation.