English Medium Class 10 - CBSE Question Bank Solutions for Science

What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper

Consider two statements A and B given below:
A: real image is always inverted
B:  virtual image is always erect
Out of these two statements:

Which one of the following materials cannot be used to make a lens?

The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.

Name the physical quantity whose unit is dioptre.

Which type of lens has (a) a positive power, and (b) a negative power?

Which of the two has a greater power: a lens of short focal length or a lens of large focal length?

How is the power of a lens related to its focal length?

Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.

The focal length of a convex lens is 25 cm. What is its power? 

What is the power of a convex lens of focal length 0.5 m?

A converging lens has focal length of 50 mm. What is the power of the lens?

What is the power of a convex lens lens whose focal length is 80 cm? 

A diverging lens has focal length of 3 cm. Calculate the power. 

The power of a lens is + 0.2 D. Calculate its focal length. 

The power of a lens is, −2 D. What is its focal length? 

What is the nature of a lens having a power of + 0.5 D?

What is the nature of a lens whose power is, −4 D?

The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?

A doctor has prescribed a corrective lens of power, −1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?