NCERT Solutions for Class 10 गणित Chapter 10 Light - Reflection And Refraction

An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror.

Analyse the following observation table showing a variation of image distance (v) with object distance (u) in the case of a convex lens and answer the questions that follow, without doing any calculations:

(a) What is the focal length of the convex lens ? Give reason in support of your answer.
(b) Write the serial number of that observation which is not correct.How did you arrive at this conclusion?
(c) Take an appropriate scale to draw a ray diagram for the observation at S. No. 4 and find the approximate value of magnification.

To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.

A concave mirror produces three times magnified image on a screen. If the object is placed 20 cm in front of the mirror, how far is the screen from the object?

In the following diagram the correctly marked angles are:

• ∠ A and ∠ e

• ∠ i, ∠ A and ∠ D

• ∠ A, ∠ r and ∠ e

• ∠ A, ∠ r and ∠ D

The correct sequencing of the angle of incidence, the angle of emergence, the angle of refraction and lateral displacement shown in the following diagram by digits 1, 2, 3 and 4 is:

• 2, 4, 1, 3

• 2, 1, 4, 3

• 1, 2, 4, 3

• 2, 1, 3, 4

A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that, he gradually moves the flame towards the lens and each time focuses the image on the screen.

(a) In which direction-toward or away from the lens, does he move the screen to focus the image?
(b) How does the size of the image change?
(c) How does the intensity of the image change as the flame moves towards the lens?
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size?

If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.

State the laws of refraction of light. Explain the term ‘absolute refractive index of a medium’ and write an expression to relate it with the speed of light in vacuum.