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### E=pc vs E=hv

Posted: Mon Oct 26, 2020 4:18 pm
Hi! When do we use the Einstein equation E=hv versus the equation E=pc?

### Re: E=pc vs E=hv

Posted: Mon Oct 26, 2020 5:01 pm
Generally, I think we will just use E=hv because it finds the energy of the photon using Plank's constant and the frequency of light.

E=pc also finds the energy of a photon, but using the speed of light and momentum of the photon instead. It probably won't be used for calculation, but it's important for the derivation of De Broglie's equation.

Hope this helps! :)

### Re: E=pc vs E=hv

Posted: Tue Oct 27, 2020 9:52 pm
I believe the Einstein equation E=hv is much more relevant for our purposes, relating energy to frequency. While both are used in energy calculations, I have not used E=pc in any textbook or sapling question so far.

### Re: E=pc vs E=hv

Posted: Thu Oct 29, 2020 12:43 am
I believe E=pc is usually used in cases like DeBroglie problems, where p=mass x velocity. E=hv is a more common formula we have been using because we are often given problems involving frequency.

### Re: E=pc vs E=hv

Posted: Thu Oct 29, 2020 2:14 am
I think we use E=hv to find the energy of a photon using Plank's constant and the frequency of light, so most of the times when we are dealing with frequency. While E=pc also finds the energy of a photon, it uses the speed of light and momentum of the photon, so it's important for De Broglie's equation.

### Re: E=pc vs E=hv

Posted: Thu Oct 29, 2020 9:04 am
E=pc is used when the mass or velocity of the electron is given in the problem, while the E=hv is used when frequency or wavelength is given.

### Re: E=pc vs E=hv

Posted: Tue Nov 03, 2020 2:52 pm
I'm pretty sure you can use whichever one you like and that it just depends on the information that you're given in the problem. Hope this helps!

### Re: E=pc vs E=hv

Posted: Tue Nov 03, 2020 2:58 pm
I agree that it definitely depends on what you're givenâ€”just make sure you know the info the problem gives you and what you want to know. Both equations are valid.

### Re: E=pc vs E=hv

Posted: Tue Nov 03, 2020 3:17 pm
Madeline Ogden 1D wrote:I'm pretty sure you can use whichever one you like and that it just depends on the information that you're given in the problem. Hope this helps!
I agree. It just depends on what the question asks and the given information.

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 8:08 am
I think both can be used to calculate the energy of an electron, it just depends on the information you're giving in the question. From my experience, I think the equation we need to be careful with is E=mc squared.

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 7:48 pm
I would say it depends on the information given to you in the problem. Generally E=pc is used when you are given mass or velocity. E=hv is used when you are given frequency or wavelength.

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 7:51 pm
As stated with the posts above, it truly depends on what the problem is asking for.

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 9:50 pm
both find similar answers, it just depends on what is given

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 9:54 pm
Hey!
My understanding is that E=hv is only used for light/photons. However, E=pc is used for these that have mass, like electrons.

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 11:34 pm
E=hv is used more for the problems with finding energy of a photon but e=pc can be used when you know momentum (mass x velocity)

### Re: E=pc vs E=hv

Posted: Sun Nov 08, 2020 11:50 pm
E = hv is only used for finding the energy of photons/light, while E = pc can be used for particles with mass.