Question

Define focal length...

Answer 1

➡️$\textbf{Focal Length}$ is the distance between $\mathsf{Pole}$ and $\mathsf{Focus}$ of a $\textbf{Spherical Mirror.}$ ✔️

➡️ Focal Length is denoted as $\mathsf{'f'}$ ✔️

Answer 2

The distance between the pole and the principal focus of a spherical mirror is known as its focal length.