Originally Posted by
crazyman2
No way, h/(lamba) is the equation for the momentum of a photon. it could also be written as hf/c. And it is derived from einsteins E=mc^2. The only way to prove a photon has momentum is by einsteins energy/mass equivalency.
Ok so p=mv, but photons don't have mass, but they do have energy. So we can use einsteins E=mc^2. Solve for mass: m=E/c^2. Substitute that into p=mv: p=(E/c^2)v. But the velocity of a photon is always c, so that cancels with 1 of the c's on the bottom creating : p=E/c. And, as i stated in the wrong place in an above post, E=hf. Substitute in for E: P=hf/c. And because v=(lambda)f and v=c then p=hf/(lambda)f. the f's cancel and you get p=h/(lambda)
according to physics 30 of course =). they could easily have lied about that haha.