Question

Prove that a ray parallel to the principal axis after reflection in concave mirror passes through its focus.

Answer 1

$$\begin{gathered} U\sin gmirrorformula,\frac{1}{f}=\frac{1}{v}+\frac{1}{u} \\ AsRaysarecomingparallelfromdis\tan tobject,u=\infty , \\ \Rightarrow \frac{1}{f}=\frac{1}{v}+\frac{1}{\infty } \\ \Rightarrow f=v, \\ Sotheimagedis\tan ceisequaltotheFocallength,(thepointwhereimageformed) \end{gathered}$$