00:01
Our question has asked us to calculate the debrilj wavelength of electrons with kinetic energy, which i call e here, for part a of 10ev.
00:10
So i converted electron volts into joules by multiplying it by 1 .6 times 10 to minus 19 joules.
00:16
So now we have the energy.
00:17
To find the debril j wavelength, we use the equation that says that lambda is equal to the planx constant h divided by the momentum of the particle p.
00:28
So the question is, what's the momentum of the particle? so energy, we'll do this over here, energy is equal to one -half mv squared.
00:40
But mass times velocity is equal to momentum.
00:44
So this is the same as one -half momentum squared over the mass.
00:53
So you can solve this for momentum squared, and you find that p is equal to the square root of two times the mass times the energy.
01:06
So now we have an expression for momentum, and we know the mass, since it's an electron, it's 9 .1 times 10 to the minus 31 kilograms.
01:13
So plugging that in, we find an expression for lambda that says that h is, or excuse me, lambda is equal to h divided by the square root of two times the mass times the energy.
01:25
So now you know why we converted to joules, so we can use si units, and we find a value for lambda equal to 0 .39 times 10 to the minus 9 meters or 0 .39, now.
01:37
Nanometers...