00:01
Here we will start with the lens equation.
00:04
1 over f equals 1 over q plus 1 over p, where f is the focal length, q is the object distance, and p is the image distance.
00:14
Then we recall that the focal length for a mirror is negative r, the radius of curvature, divided by 2.
00:22
It's for a spherical mirror.
00:30
Plugging this into the equation, we have negative 2 over r, since we must take the reciprocal, equals 1 over q plus 1 over p.
00:41
Okay, so this is for a spherically shaped mirror with some radius r.
00:49
We're curious what happens when we have a planar mirror instead of a spherical mirror.
00:56
To use this equation, we have to figure out when a spherical mirror will become like a planar mirror.
01:04
This occurs when you increase the radius drastically.
01:10
For instance, if we increase the radius a little bit, we have something that resembles this...