If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at 30 cm above the paper. If…

If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at $\displaystyle 30$ cm above the paper. If the radius of curvature of the lens is $\displaystyle 60$ cm then the refractive index of the lens material is $\displaystyle \frac{\alpha}{10}$. The value of $\displaystyle \alpha$ is $\displaystyle \_\_\_\_$.