00:01
Here we have a pair electron positron at rest, and then they vanish and give rise to two photons.
00:12
And we're tasked in this exercise with calculating the wavelength of these two photons, assuming that their wavelength is the same.
00:24
So what we're going to have to do is calculate the initial energy of the system, since the system is at rest, both the electron and the positron are at rest, we can calculate the energy of the system to be the rest energy of the electron, which is mec squared.
00:46
M .e is the mass of the electron, plus the energy, the rest energy of the positron, and the rest energy of the positron is the same as the one of the electron.
00:57
So it's going to be 2 m .e .c.
01:00
Squared.
01:01
And now we can calculate this as two times.
01:08
Remember that m .e.
01:12
Is 0 .51 meg electron volts per c squared times c squared.
01:20
So the c squared is cancel out...