E=hv vs E=pc?

[Ami_Pant_4G]

What is the difference between E=hv and E=pc? The notes made it seem that thy were both used to calculate energy of the photon, so would that mean the only difference is the circumstance in which you would use them?

[AGulati_4A]

E= P*C is probably most likely not used in calculations. I think when it could be important is in the derivation of the De Broglie wave equation, which converts the P into mv and C into (lambda)(frequency) in order to find the De Broglie equation

[TarynD_1I]

E=hv is used to find the energy of a photon using Planck's constant and frequency of light.
E=pc is used to find the energy of a photon using the speed of light and the momentum of a photon. I'm pretty sure we only use E=pc when momentum of the photon is provided.

[jvera4b]

E=hv would be used if the frequency is given or you can find it by manipulating c=(lambda)v, E=pc would be used when the momentum cana be found such as when the velocity or momentum is given.

[RitaThomas_3G]

E=hv is used to find the energy of a photon using Planck's constant and frequency of light.
E=pc is used to find the energy of a photon using the speed of light and the momentum of a photon. I'm pretty sure we only use E=pc when momentum of the photon is provided.

Hey! Just adding on to what was said here, in E = pc, p is for the momentum of the photon, and c is for the speed of light. Essentially, both of these equations are just different ways to solve for energy of the particle (E), it just depends on what is given in the problem or what you can solve for.

[Mackenzie Stockton 2H]

Both equations are valid for calculating the energy of the photon. You would use either equation depending on what variables you are given.

[Reese_Gover2K]

Yep you got it! They both calculate the same thing but the one you use depends on the information you're given. You'd use E=pc if you're given the momentum of the photon and you'd use E=hv if you're given the frequency.

[Rohit Srinivas 2D]

How would we calculate the momentum of a photon? Is it a similar calculation to that of an electron except we use the mass of a photon instead? What would be the units? thanks.

[Scot Widjaja Dis 1J]

I guess it would depend on what variables you were given in the problem. If a question gave you the photon's frequency or wavelength then you would use E=hv. However, if a question gave you the particles mass and velocity, then you would use E=pc. Hope this helps.