Science (English Medium) Class 12 - CBSE Important Questions for Physics

What is the cause of dispersion of light

A ray of light incident normally on one face of a right isosceles prism is totally reflected, as shown in fig. What must be the minimum value of refractive index of glass? Give relevant calculations.

Using mirror formula, explain why does a convex mirror always produce a virtual image.

Figure shows a ray of light passing through a prism. If the refracted ray QR is parallel to the base BC, show that (i) r₁ = r₂ = A/2 and (ii) angle of minimum deviation, D_m = 2i − A.

Draw a labelled ray diagram of an astronomical telescope to show the image formation of a distant object. Write the main considerations required in selecting the objective and eyepiece lenses in order to have large magnifying power and high resolution of the telescope.

A compound microscope has an objective of focal length 1.25 cm and eyepiece of focal length 5 cm. A small object is kept at 2.5 cm from the objective. If the final image formed is at infinity, find the distance between the objective and the eyepiece ?

Draw a labeled ray diagram of a reflecting telescope. Mention its two advantages over the refracting telescope.

How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.

Define power of a lens. Write its units. Deduce the relation `1/f =1/f_1  +1/f_2`for two thin lenses kept in contact coaxially.

Draw a labelled ray diagram of an astronomical telescope in the near point adjustment position. A giant refracting telescope at an observatory has an objective lens of focal length 15 m and an eyepiece of focal length 1.0 cm. If this telescope is used to view the Moon, find the diameter of the image of the Moon formed by the objective lens. The diameter of the Moon is `3.48 xx 10^6`m, and the radius of the lunar orbit is `3.48 xx 10^8`m.

Answer the following question.
Under what conditions is the phenomenon of total internal reflection of light observed? Obtain the relation between the critical angle of incidence and the refractive index of the medium.

Answer the following question.
Three lenses of focal length +10 cm, —10 cm and +30 cm are arranged coaxially as in the figure given below. Find the position of the final image formed by the combination. 

Photo diodes are used to detect ______.

With the help of a ray diagram, obtain the relation between its focal length and radius of curvature.

Define the term ‘resolving power of a telescope’. 

A screen is placed 80 cm from an object. The image of the object on the screen is formed by a convex lens placed between them at two different locations separated by a distance 20 cm. determine the focal length of the lens.

Define the term ‘focal length of a mirror’.

Draw a ray diagram of Astronomical Telescope for the final image formed at infinity

An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is

1. negative and
2. positive.

In the given figure the radius of curvature of the curved face in the planoconvex and the planoconcave lens is 15 cm each. The refractive index of the material of the lenses is 1.5. Find the final position of the image formed.