Science (English Medium) कक्षा १२ - CBSE Important Questions

A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at

1. the least distance of distinct vision (25 cm), and
2. infinity?

What is the magnifying power of the microscope in each case?

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.

Use the mirror equation to deduce that an object placed between the pole and focus of a concave mirror produces a virtual and enlarged image.

You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct a compound microscope?

Define resolving power of a microscope and write one factor on which it depends

Define the magnifying power of a compound microscope when the final image is formed at infinity. Why must both the objective and the eyepiece of a compound microscope has short focal lengths? Explain.

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

When are two objects just resolved? Explain.

How can the resolving power of a compound microscope be increased? Use relevant formula to support 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

Show with the help of a diagram, how unpolarised light from Sun gets linearly polarised by scattering.

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?

Does the magnifying power of a microscope depend on the colour of the light used? Justify your answer.

Use the mirror equation to show that an object placed between f and 2f of a concave mirror forms an image beyond 2f.

 Write two points of difference between the phenomena of interference and diffraction.

Draw the ray diagram showing refraction of light through a glass prism and hence obtain the relation between the refractive index μ of the prism, angle of prism and angle of minimum deviation.

Describe an activity to show that the colours of white light splitted by a glass prism can be recombined to get white light by another identical glass prism. Also, draw a ray diagram to show the recombination of the spectrum of white light.

In the following diagram, an object 'O' is placed 15 cm in front of a convex lens L₁ of focal length 20 cm and the final image is formed at I at a distance of 80 cm from the second lens L₂. Find the focal length of the lens L₂.

Why does the Sun look reddish at sunset or sunrise ?