Class 12 Ray Optics And Optical Instruments CBSE Questions & Answers

A plano-convex lens is made of glass of refractive index 1.5.The focal length ƒ of the lens and radius of curvature R of its curved face are related as

A thin convergent glass lens (\({\mu _{\rm{g}}}\) = 1.5 ) has a power of + 5.0 D. When this lens is immersed in a liquid of refractive index \({\mu _o}\) it acts as a divergent lens of focal length 100 cm. The value of \({\mu _{\rm{1}}}\)must be

What is the relation between refractive indices \(\mu \), \(\mu \) 1 and \(\mu \) 2 if the behavior of light rays is as shown in the following figure?

A lens forms a sharp image on a screen. On inserting a parallel sided glass slab between the lens and the screen, it is found necessary to move the screen a distance d away from the lens in order to focus the image sharply. If the refractive index of glass relative to air is μ, the thickness of the glass slab is given by

A convex lens is placed between an object and a screen which are a fixed distance apart. For one position of the lens the magnification of the image obtained on the screen is m1. When the lens is moved by a distance d, the magnification of the image obtained on the same screen is \({{\rm{m}}_{\rm{2}}}\). The focal length of the lens is (\({{\rm{m}}_{\rm{1}}} > {\rm{ }}{{\rm{m}}_{\rm{2}}}\))

An object and a screen are mounted on an optical bench and a converging lens is placed between them so that a sharp image is received on the screen. The linear magnification of the image is 2.5. The lens is now moved 30 cm nearer the screen and a sharp image is again formed on the screen. The focal length of the lens is

A lamp and a screen are set up 100 cm apart and a convex lens is placed between them. The two positions of the lens forming real images on the screen are 40 cm apart. What is the focal length of the lens ?

A convex lens forms a real image of an object on a screen; the magnification of the image being 3/2. The object and the screen are kept fixed and the lens is moved through a distance of 16 cm when a sharp image is again formed on the screen; the magnification now being 2/3. What is the focal length of the lens?

An object is placed at a distance of 10 cm from a co-axial combination of two lenses A and B in contact. The combination forms a real image three times the size of the object. If lens B is concave with a focal length of 30 cm, what is the nature and focal length of lens A ?

A plano-convex lens acts like a concave mirror of 28 cm focal length when its plane surface is silvered and like a concave mirror of 10 cm focal length when its curved surface is silvered. What is the refractive index of the material of the lens?

A pin is placed 10 cm in front of a convex lens of focal length 20 cm and refractive index 1.5. The surface of the lens farther away from the pin is silvered and has a radius of curvature of 22 cm. How far from the lens is the final image formed?

A telescope, when in normal adjustment, has a magnifying power of 6 and the objective and the eye-piece are 14 cm apart The focal lengths of the eye-piece and the objective respectively are

A telescope has an objective of focal length 100 cm and an eye-piece of focal length 5 cm. What is the magnifying power of the telescope when it is in normal adjustment?

The objective of a telescope has a focal length of 1.2 m. It is used to view a 10.0 m tall tower 2 km away. What is the height of the image of the tower formed by the objective?

A giant telescope in an observatory has an objective of focal length 19 m and an eye-piece of focal length 1.0 cm. In normal adjustment, the telescope is used to view the moon. What is the diameter of the image of the moon formed by the objective? The diameter of the moon is 3.5 \( \times {\rm{ 1}}{0^{\rm{6}}}\) m and the radius of the lunar orbit round the earth is 3.8 \( \times {\rm{ 1}}{0^{\rm{8}}}\) m