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When do you use light equations?

Posted: Mon Nov 04, 2019 9:19 pm
Hey guys,
I'm confused as to when use light equations (c=wavelengthxfrequency, and E=hc/wavelength) because some questions provide wavelengths already and it's technically not speed of light being used. Thank you!

Re: When do you use light equations?

Posted: Mon Nov 04, 2019 9:43 pm
I'm confused about this too. in some of the review sessions, they mentioned that there were only certain instances where the equation could be used. And you needed to know when.

Re: When do you use light equations?

Posted: Mon Nov 04, 2019 9:52 pm
If the value given is wavelength for an electron, frequency cannot be calculated with this equation because the constant c is the speed of light, and it is impossible for an electron to move at the speed of light. If the value given is wavelength for a photon, go ahead and use it. For electrons, we use de Broglie's equation.

Re: When do you use light equations?

Posted: Tue Nov 05, 2019 9:54 pm
Whenever you're dealing with photons and electromagnetic radiation, you use E = hv, c = lambda x frequency, etc. However, when you're dealing with particles WITH mass (like electrons, protons, neutrons, etc), then you'd use de Broglie's equation, λ = h / p --> λ = h / mv.

You can't use E = hv or c = λv to work with particles with mass considering that particles with mass have their own unique velocities, while the speed of light remains constant (c = 2.98 x 10^8 m/s).