00:01
So in this class string, we have an electron, and we want to do two things about it.
00:07
Part a, we want to accelerate that electron from a speed of 3 .00 times 10 to 6 meter per second to 8 .00 times 10 to 6 meters per second.
00:20
And we want to know what is a potential difference required to accomplish this.
00:25
And part b, we want to know what is, again, what is a potential difference? that will bring it from 8 .00 times 10 to the 6 meters per second to a stop.
00:38
And to do this, we need to use the energy conservation.
00:42
And we know that when electron is speed up or slowdown, what is changing is the kinetic energy of it.
00:50
And because due to the energy conservation, whatever changes of the kinetic energy, it has to be caused by the potential energy.
01:01
The potential energy and kinetic energy will have to add up to be the same.
01:08
So in other words, we know at two points of u1 plus k1 equals v2 plus k2, or actually i should write, it's u1 plus the kinetic energy plus the potential energy at one point is equal to the potential energy plus kinetic energy at the second point.
01:35
So we want to know the potential difference.
01:40
So we want to know delta v equals v1 minus v2 equals u1 minus u2 over q because potential is potential energy divided by q and this is equal to k q minus k1 because this u1 minus u2 equals k2 minus k1 divided by q.
02:03
So now we can plug in all the numbers here.
02:09
We have kinetic energy is one half of mv square, one half an e of v22 minus v1 square over charge of electron.
02:28
Now we're putting some numbers.
02:31
I'll move this down.
02:34
We were putting some numbers.
02:37
One half of the mass of an electron is, you can look it up.
02:43
I think it's 3...