Ray Optics and Optical Instruments PYQs

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since

A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance d between them. If a parallel beam of light falling on 'A' leaves 'B' as a parallel beam, then 'd' is:

A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror is kept perpendicular to the principal axis and at a distance of 40 cm from the lens, the final image would be formed at a distance of:

In an astronomical telescope in normal adjustment, a straight black line of length $L$ is drawn on the inside part of the objective lens. The eyepiece forms a real image of this line. The length of this image is $l$. The magnification of the telescope is:

A beam of light consisting of red, green and blue colours is incident on a right-angled prism. The refractive indices of the material of the prism for the red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. The prism will:

A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices $\mu_1$ and $\mu_2$, and $R$ is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is

For a normal eye, the cornea of eye provides a converging power of $40\,D$ and the eye lens behind the cornea is $20\,D$. Using this information, the distance between retina and the cornea-eye lens system can be estimated to be

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:

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 end closer to the pole is 20 cm away from the mirror. The length of the image is: