Question

Q). Explain how?
Radius of curvature of a plane mirror m = $\infty$ (infinite)
Focal length of a plane mirror = $\infty$

Answer 1

Dear student,

Well, the radius determines how much the mirror will curve. If the radius is really small, the mirror will be really curved; if the radius is large, the mirror will be less curved.
Consider how curved a mirror with a radius of curvature the size of a marble would be, versus a mirror with a radius of curvature the size of a beach ball. Now consider how curved a mirror with a radius of curvature the size of the earth--and imagine how flat that would seem if you stood on it.
In fact, the larger the radius of curvature, the flatter the surface will appear. Thus, a perfectly flat surface will occur when the radius of curvature equals infinity. And when R is infinity then f will also become infinity.

Regards