00:01
So here we are given a disk of radius, let's say, capital r equals to 0 .600 meter, revolving a ordnate center.
00:10
Okay.
00:11
Now we have to find the distance at which the electric field becomes half the electric field at a center of that disk.
00:21
So for this, first of all, let us talk about the concept behind us.
00:25
So let's suppose this is nothing but what, the circular disk.
00:29
This is what the center of the disk and this much of length will be radius for the disk.
00:35
Now let at the point of center of the disk, the electric field is easy.
00:42
Now we suppose a point p above to the center of the disk, which is at a distance of dirt which we have to find here according to question.
00:56
Now at this point, let the electric field is nothing but what, ep.
01:03
Now if you see, according to question, it is stated that the electric field at that point, ep is one half to the electric field at the center of the disk.
01:14
So from here what we get, we get the ratio of ep by ec.
01:19
This should be quashed to what that is one half.
01:23
Now, at a point on the axis of uniform, charge, disc which is at a distance of z, the center of the disk, the magnitude of electric field can be given by equals to sigma upon two epsilon node in bracket 1 minus z upon under root of z square plus r square.
01:50
Where r is the radius of the disk, sigma is surface charged density of the disk.
01:57
Now the magnitude off -field at the center of the disk is ec means for the value of z to be equals to 0.
02:08
So in that case this whole term is going to be 0.
02:11
So ec will come out to be sigma upon 2 -e -0.
02:19
And similarly, ep would be quest to how much? that is sigma upon 2 -epsilon node...