00:01
So we have here a concave mirror and what we want to do is we want to show that for a ray that's parallel to the principal axis, it's reflected ray.
00:10
It's going to pass through a focal point f that is a distance of one half the radius of the curvature of the mirror.
00:18
And the radius of that curvature is going to be equal to the distance between point c and point v where point c is the center of the curvature.
00:29
So what we see here is that we have this ray that's coming in incident to point a, and this line here going through f represents the reflected angle.
00:40
And we know that the line between point a and point c represents the line that's normal from the point where the light is incident to the mirror.
00:53
So now that we've established that line ac is normal to the mirror, we can apply the fact that we know that the angle of incidence is equal to the angle of reflection, which is angle theta 1 and theta 2 respectively.
01:11
So we can say that theta 1 is equal to theta 2 due to that rule.
01:18
And if we see here, we're looking at the principal axis and this ray of light, which is parallel to the principal axis.
01:25
So we have two parallel lines.
01:26
And we have this line...