Refractive index of a glass convex lens is 1.5 . The radius of curvature of each of the two surfaces of the lens is 40 cm . The ratio of the power of the lens when immersed in a liquid of refractive index 1.25 to that when placed in air is

A monochromatic ray of light is incident normally on a thin prism of refracting angle A . The ray is deviated through an angle $(1.15)^{\circ}$ in passing through the prism. The ray reflected internally from the second face emerges from the first face making an angle of $(6.3)^{\circ}$ with the incident ray. The refractive index of the prism is

A glass cube of length 21 cm has a small air bubble trapped inside. When viewed normally from the opposite face, its apparent distance is 6 cm . The refractive index of glass and the actual distance of the air bubble from the first surface respectively are

The image of an object approaching a convex mirror of radius of curvature 20 m along its optical axis is observed to move from $\frac{25}{3} \mathrm{~m}$ to $\frac{50}{7} \mathrm{~m}$ in 30 second. The speed of the object in $\mathrm{km} / \mathrm{hr}$ is