Science (English Medium) Class 12 - CBSE Important Questions

Identify the part of the electromagnetic spectrum which:

1. produces the heating effect.
2. is absorbed by the ozone layer in the atmosphere.
3. is used for studying crystal structure.

Write any one method of the production of each of the above radiations.

Draw a labeled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power.

1. A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?
2. If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.48 × 10⁶ m, and the radius of lunar orbit is 3.8 × 10⁸ m.

Why should the objective of a telescope have large focal length and large aperture? Justify your answer. 

Draw a ray diagram depicting the formation of the image by an astronomical telescope in normal adjustment.

You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope ? Give reason

You are given three lenses of power 0.5 D, 4 D, and 10 D to design a telescope.

1) Which lenses should be used as objective and eyepiece? Justify your answer.

2) Why is the aperture of the objective preferred to be large?

An equiconvex lens of focal length 'f' is cut into two identical plane convex lenses. How will the power of each part be related to the focal length of the original lens ?

A double convex lens of + 5 D is made of glass of refractive index 1.55 with both faces of equal radii of curvature. Find the value of its radius of curvature.

Draw a ray diagram showing the image formation of a distant object by a refracting telescope ?

Write the two important factors considered to increase the magnifying power?

Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?

"A telescope resolves whereas a microscope magnifies." Justify this statement ?

Define its magnifying power and write the expression for it?

A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece lens of focal length 1.0 cm is used, find the angular magnification of the telescope. If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.42 × 10⁶ m and the radius of the lunar orbit is 3.8 × 10⁸ m.

Calculate the speed of light in a medium whose critical angle is 30° ?

Find the radius of curvature of the convex surface of a plano-convex lens, whose focal length is 0.3 m and the refractive index of the material of the lens is 1.5.

What type of wavefront will emerge from a (i) point source, and (ii) distance light source?

Use the above relation to obtain the condition on the position of the object and the radius of curvature in terms of n₁and n₂ when the real image is formed.

Answer the following question.
An optical instrument uses a lens of 100 D for the objective lens and 50 D for its eyepiece. When the tube length is kept at 20 cm, the final image is formed at infinity.
(a) Identify the optical instrument.
(b) Calculate the magnification produced by the instrument.