A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its enf closer to the pole is 20 cm away from the mirror. The length of the image is

For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index.

The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are

A concave mirror of focal length $$f$$₁ is placed at a distance of d from a convex lens of focal length $$f$$₂. A beam of light coming from infinity and falling on this convex lens $$-$$ concave mirror combination returns to infinity. The distance d must equal