NCERT Class X Science Class: Chapter –10. Light – Reflection and Refraction – Part-6

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Question 25:

A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?

Answer:

Statement is correct if the object is placed within from the lens in the first case and between in the second case.

Question 26:

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

Answer:

Sudha should move the screen towards the lens so as to obtain a clear image of the building. The approximate focal length of this lens will be l5 cm. The rays of light coming from distant object such as a tree (or a distant building or electricity pole) can be considered to be parallel to each other. When parallel rays of light are incident on a convex lens, the rays, after refraction, converge at focus on the other side of the lens.

Question 27:

How are power and focal length of a lens related? You are provided with two lenses of focal length respectively. Which lens will you use to obtain more convergent light?

Answer:

The power of a lens is related to its focal length as

Power of a lens is inversely proportional to its focal length therefore lens having focal length of will provide more convergence.

Question 28:

Under what condition in an arrangement of two plane mirrors, incident ray and reflected ray will always be parallel to each other, whatever may be angle of incidence. Show the same with the help of diagram.

Answer:

When two plane mirrors are placed at right angle to each other than the incident and reflected rays will always be parallel to each other

Double reflection

Double Reflection

Double reflection

Question 29:

Draw a ray diagram showing the path of rays of light when it enters with oblique incidence (i) From air into water.

(ii) From water into air.

Answer:

When ray of light enters from air into water, it bends towards the normal and When ray of light enters from water into air, it bends away from the normal as shown in below figure:

Refraction at air water boundry

Refraction at Air Water Boundry

Refraction at air water boundry

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