00:01
Okay, so here we've got some questions about electric field lines that we want to say whether they're true or false.
00:06
So the first one is electric field lines radiate away from positive charges and towards negative charges.
00:10
Now, this is true.
00:11
We draw electric field lines so that they go in the direction a positive charge would move in.
00:16
So, for instance, if we have a point positive charge, then it will repel our imaginary positive charge.
00:23
And so this positive charge would move away.
00:26
And so we point the electric field lines away from the central point charge.
00:30
Similarly, with a negative point charge, a positive charge placed around it would move towards it.
00:35
And so these would be the field lines in this case.
00:40
Question two, electric field is always perpendicular to equipotential lines.
00:44
This is also true.
00:46
So equipotential lines are lines with the magnitude of the electric field being the same.
00:59
So in the example above, with our point charges, since we know that the potential, potential goes like the product of the two charges over the distance between them, we can see that if we place a test charge at any point, so we put a test charge here, this red dot, you can see that any point on this circle is going to have the exact same magnetic field if it's got the same charge because it's at the same distance from the origin from the point charge.
01:37
So this is just a lot of the same charge.
01:38
An example of why this is true, but it's two more generally.
01:41
Okay, point three, the electric field points in the direction of increasing electric potential...