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