00:01
So in this problem, we're looking at an isolated electron.
00:03
You're asking why it is not capable of emitting a single photon.
00:08
So that's not the situation, this figure on the left.
00:12
That's for part b.
00:15
So the first thing we're going to look at is conservation of energy.
00:19
You have the total energy of the system is the electron plus the photon energy, but we began with just an electron.
00:27
And the electron in its own frame of reference is stationary.
00:43
Let's see, we could write that as hc divided by lambda.
00:51
So you have an isolate electron, and it's a photon.
00:57
Where is the energy for the photon going to come from? because the original total energy of the system was mc squared.
01:06
So that would have to equal zero if isolated.
01:14
Electron.
01:17
So what you would have to have is the, say, the electron getting annihilated and releasing its energy as photon.
01:25
But then even in that situation, you ask what, why can't you have just one photon? so we're beginning with the situation where the total momentum of the system is zero.
01:41
So the electron is initially stationary...