00:01
So we have this system where we have a sphere in the middle, and that has some radius r1, and then we have some open space surrounding that sphere, and then we have some concentric spherical shell.
00:22
And the first layer of the shell is at r2, and the next layer, the outer layer, it ends, at r3.
00:33
So i'll shade in the conducting sphere and the conducting shell, because that will be important.
00:46
And so we know that r1 is 4 centimeters or 0 .04 meters.
00:56
We know that r2 is 2 times r1, so that 0 .08 meters.
01:05
And we know that r3 is 2 .5 times r1.
01:12
So that would be 1 meter, sorry, 0 .1 meters.
01:19
And the sphere on the inside has some charge q1 on it.
01:28
And that charge q1 is positive 4 times 10 to the negative 9th coulum.
01:35
And the net charge on the concentric shell.
01:40
So the net charge on the concentric shell is q2, and that net charge is negative 2 .5 times 10 to the negative 9th kulams.
01:55
So for part a, we would like to know the magnitude of the electric field at the following radial distance.
02:04
The radial distance is 2 .4 times r1.
02:10
This would imply that it is inside the spherical shell, and that would imply that it is inside a conductor.
02:22
And inside a conductor, e -field equals zero.
02:29
That is just a basic rule for conductors.
02:34
Then we would like to know the e -field at a radius of 3 .8r1, which equals 0 .152 meters.
02:49
Now, i'll draw this in red.
02:51
This would be outside the entire system.
02:57
And so because of that, we can use gouse's law.
03:02
And when we use gouss ' law, we know that the integral of e -field, dotted with the da, so the area or the tiny little bit of area that you are integrating over.
03:22
This is equal to the charge that is enclosed by your surface divided by epsilon knot.
03:31
And we know that efield coming from any spherical object will be constant as it passes that gaussian surface...