00:01
Okay, so we have an electric potential energy conceptual question, and then we're building on those concepts with some numerical questions afterwards.
00:11
So first, if we have an electron is released from rest in a constant electric field, has the electric potential energy associated with the electron and the kinetic energy of the electron change with time.
00:22
So if we're starting from rest, the kinetic energy is going to start as zero, and then as this thing starts moving, our kinetic energy is going to end.
00:30
Increase.
00:32
Kinetic energy is never negative.
00:33
So from the answer choices that we have, we're going to select that the kinetic energy becomes more positive.
00:40
And then from the second equation that i have written out here, the change in kinetic energy is equal to the negative change in potential energy.
00:51
So if the kinetic energy is becoming more positive, then that means that the electric potential on a g must become more negative to be able to compensate.
01:01
So those are going to be the two answer choices that we would select.
01:05
Okay, and then for the practice it, our first question is that we have a proton released from rest at x equals 0 .21, or negative 0 .21 centimeters.
01:20
So i already started drawing this.
01:23
So we've got our proton, we've got our electric field, the magnitude of the electric field is, i'll write that over here, 1 .48 times 10 to the 3 newtons per coulom.
01:44
The elementary charge is 1 .6 times 10 to the minus 19 coolams, and i think that's all we need for the time being.
01:54
And we want to know the change in potential energy when the proton reaches x equals 0 .5 .43 centimeters.
02:05
So i'm also going to put this, i'm going to call this x1.
02:10
We're also going to put this into meters just by moving that decimal place to the left by 2.
02:18
And then it's going to end up somewhere over here.
02:23
I'll draw this in green.
02:26
Our x2 is equal to 5 .5 .5 .4 centimeters.
02:32
And again, we're going to move that decimal place to the left, so we can convert that into meters.
02:39
And then we're just going to use that first equation that i have written there for change in potential energy in terms of the electric field...