To find the focal length of a convex mirror, a student records the following data. The focal length

Question

To find the focal length of a convex mirror, a student records the following data. The focal length of the convex lens is $f_{1}$ and that of mirror is $f_{2}$. Then taking index correction to be negligibly small, $f_{1}$ and $f_{2}$ are close to\

Professor PC Thomas Classes · Answer

(a) : The given figures shows the experimental set up to find the focal length of convex mirror using convex lens.\ $	herefore \quad$ For lens, $u_{1}=-(32.2-22.2) \mathrm{cm}$
$ \begin{aligned} & \quad=-10 \mathrm{~cm} \ & \begin{array}{l} v_{1}=(71.2-32.2) \mathrm{cm}=39 \mathrm{~cm} \ 	herefore \quad \frac{1}{f_{1}}=\frac{1}{v_{1}}-\frac{1}{u_{1}}=\frac{1}{39}+\frac{1}{10}=\frac{49}{390} \end{array} \ & 	ext { or } f_{1}=\frac{390}{49} \mathrm{~cm} \approx 7.8 \mathrm{~cm} \ & \begin{aligned} 	herefore \quad 	ext { For mirror, } R & =(71.2-45.8) \mathrm{cm} \ & =25.4 \mathrm{~cm} \end{aligned} \ & 	ext { or } f_{2}=\frac{25.4}{2} \mathrm{~cm}=12.7 \mathrm{~cm} \end{aligned} $