The distance between the objective and eye piece of astronomical telescope in normal adjustment is 27 cm and its magnifying power is 8 . What is the focal length of the eye piece?

The ratio of the angle of deviation produced by a thin prism, when it is placed in air to the angle of deviation produced when it is immersed in water of refractive index $\frac{4}{3}$ is:

An object placed 40 cm in front of a thin convex lens is moved to 60 cm from the lens. If the focal length of the lens is 30 cm the ratio of magnification of the image at the initial position to the final position is:

An object is placed 25 cm in front of a fully silvered concave mirror of focal length 15 cm . A plane mirror is placed 35 cm behind the concave mirror on the side opposite to the object. The final image after reflection first from the concave mirror and then from the plane mirror is formed at: