00:01
So in this question, we need to use the fact that for a relativistic particle, the energy is the kinetic energy plus the mass energy, which is mc squared.
00:13
So in this question, we have that the total energy is the energy of a photon, which is 2 .5 mega electron volts.
00:22
And we're told that the kinetic energy, so the photon goes to an electron and a positron, and the kinetic energy of the electron is 0 .739 megaelectron.
00:33
Volts.
00:36
Now we can work out the mass energy of an electron.
00:40
M -e -c -squared is going to be the mass of the electron, which is 9 .11 times 10 to the minus 31.
00:49
We need to multiply by c -squared, which is 3 times 10 to the 8, and squaring that.
00:58
And then we want to put this in electron volts, so we divide by the charge on the electron, and we want to put it in mega -electron so we also have to divide by 10 to the 6.
01:10
And now this is going to have units of mega electron volts...