A ray of light travels from a denser medium to a rarer medium. The reflected and the refracted rays are perpendicular to each other. If '$$r$$' and '$$r_1$$' are the angle of reflection and refraction respectively and '$$\mathrm{C}$$' is the critical angle, then the angle of incidence is

A convex lens of focal length 'F' produces a real image 'n' times the size of the object. The image distance is

A ray of light is incident at an angle $i$ on one face of a thin angled prism. The ray emerges normally from the other face. Refractive inder of the glass prims is $n$ and angle of prism is $A$. The value of $i$ is

An object is clearly seen through an astronomical telescope of length 50 cm . The focal lengths of its objective and eye-piece respectively, can be