HW Achieve #13

[audreywang3C]

For question 13, I understand how to calculate the energy of the photon, but I'm confused on the energy of the electron.

I started out using the E=pc equation and De Broglie wavelength = h/p to get energy = hc/wavelength, but it said the answer was incorrect. The explanation said to use the KE equation, E= 1/2mv^2.

Can anyone explain why we can't use the E=pc equation for electrons? In which situations can we use the equation, and in which situations can we not? Thanks!

[Sherri Xu 2B]

I believe E=pc is for particles with no resting mass, like a photon. KE=1/2 mv^2 would be for particles with a resting mass, in this case, an electron.

[morgantolbert]

Hi! So I used that same equation, E = pc, and substituted just as you did, so it can work! I did E = pc, but since we don't have p, I went ahead and solved for p using
1.9 * 10^-6m (wavelength) = 6.626 * 10^-34 (plank's constant) / p

I then used that p value and multiplied it by "c" or the speed of light (3*10^8) and got both answers!

Maybe you rounded too much or some small error but hopefully this works and makes sense!