00:01
So if we break down and prove that c is equal to r is equal to 2f using the diagrams and the approach, we can make some assumptions that we are dealing with a concave spherical mirror.
00:28
The object is placed on the principal axis, and the rays obey the law of reflection, angle, of incidence is equal to angle of reflection.
00:44
So we start with our diagram analysis.
00:48
So the ray through the center, we can draw a ray from the object's tip that passes through the center of curvature c.
01:00
This ray is perpendicular to the mirror surface at the point of incidence.
01:05
Therefore, it reflects back on itself along the same path.
01:10
So we have similar triangle.
01:12
We could draw the object height h and the object distance s and the ray passing through c.
01:21
So these will be outlined here in a moment.
01:30
So if we combine our ratios, you would have h over h prime is equal to s over s prime, and then h over h prime is equal to s over f.
02:00
That's our focal point.
02:02
So we have to equate these two s over s prime, is equal to s over f.
02:15
So then if we rearrange this, we can get s is equal to f...