CBSE Class 10 Science 2024-25: Chapter 9 Light-Reflection and Refraction Competency-Based Questions with Answers; Download Free PDF

As the CBSE Class 10 board exams get closer, it’s important for students to understand the new exam pattern. Starting in the 2024-25 school year, CBSE will include 50% more competency-based questions. These questions will be both multiple choice and written, focusing on how to use what students have learned in real-life situations.

This article explores Chapter 9: Light-Reflection and Refraction. It highlights key competency-based questions and provides answers to help students succeed. Prepare for your CBSE Class 10 Science exams with important competency-based questions from Chapter 9: Light-Reflection and Refraction.

CBSE Class 10 Science Chapter 9: Light-Reflection and Refraction Important Competency-Based Questions

Q.1 Which of the following characteristics of a spherical mirror is given by the ratio of the size of the image to the size of the object?

A. aperture
B. magnification
C. focal length
D. radius of curvature

Answer. B. magnification

Q.2 Which of the following does the negative sign in the power -3D signify?

A. The focus is on the same side of the lens as the object.
B. The focus is on the opposite side of the lens as the object.
C. The principal focus is situated outside the principal axis.
D. The focal length on one side of the lens is smaller than that on the other.

Answer. A. The focus is on the same side of the lens as the object.

Q.3 Which among the two lenses with power- 3D AND 4D respectively can form a real image?

A. only the lens with power -3 D
B. only the lens with power 4 D
C. both the lenses
D. neither of the lenses

Answer. B. only the lens with power 4 D

Q: 4 Two convex lenses P and Q have focal length 0.50 m and 0.40 m respectively. Which of the following is TRUE about the combined power of the two lenses?
1. P is equal to 4.5 D.
2. P is less than 4.5 D.
3. P is more than 4.5 D.
4. P cannot be determined from the information given.

Answer. 3.

Q: 5 When an incident ray of light enters a medium from air, it bends towards the normal.

Which of the following is TRUE about the refractive index of the medium (nm) as compared to the refractive index of air (na)?

1. nm is equal to na.
2. nm is less than na.
3. nm is more than na.
4. (The refractive indices cannot be compared based on the given information.)

Answer. 3

Q: 6 What is the term used for the distance between the mirror and the paper?

1. radius of curvature
3. principal axis
2. principal focus
4. focal length

Answer. 4

Q: 7 What kind of image would be formed on the paper?

1. real and diminished
3. virtual and diminished
2. real and enlarged
4. virtual and enlarged

Answer. 1

Q: 8 The eyeball of a person has become slightly larger. Which kind of lens should the person wear to correct the defect in the vision caused by this change in the size of the eyeball?

Answer. concave lens

Q: 9 The images formed by an ordinary convex lens suffer from a defect, called chromatic coloured edges in the images. This happens because light rays of different colours bend differently as they enter and leave the lens.

If a parallel white light beam passes through a convex lens, the light of which colour (among violet to red in the spectrum) will converge at a point closest to the lens? Justify your answer.

Answer. violet

because it will bend the most after refraction
OR
because glass has the highest refractive index for violet coloured light

Q: 10 Smriti is looking at herself in a convex mirror in a science museum, standing 2 m away from the mirror. Her image appears to be around half her actual height. Estimate the focal length of the mirror.

Answer. Identifying object distance as -2 m

Finding out image distance as +1 m using magnification formula

Using the correct formula (1/u + 1/v1/f) [0.5 marks]
Calculating focal length as +2 m, using the formula [1 marks]

Q: 11 (a) Copy the scaled ray diagram given below. Draw more required incident rays from the pencil to illustrate the formation of the image of the pencil by the convex lens of focal length 3 cm.

Your completed diagram should show the image of the whole pencil.

(Note: Assume that the lens in the diagram is a thin lens.)

(b) What is the distance of the image of the pointed end of the pencil from the lens?
(c) What is the length of the image of the pencil?

Answer. (a) Correct completed ray diagram should include the following:
- another correctly drawn incident ray from the pointed end of the pencil [1 mark]
- two correctly drawn incident rays from the blunt/rear end of the pencil [2 marks]
- correctly drawn image of the pencil using the point images of the front and rear ends of the pencil [1 mark]

(b) 7.5 cm (with an error margin of 0.5 cm)

(c) 3.6 cm (with an error margin of 0.4 cm)

Q: 12 Manju has two convex lenses P and Q made of the same material as shown in the figure.

She is looking at printed text on a page using lens P. She notices that when she slowly takes the lens away from the page, the text turns upside down when the lens crosses distance of 10 cm from the page.

(a) Which characteristic of lens P does the distance 10 cm signify?
(b) If Manju does the same with lens Q, at what distance will the inversion of the image happen - less than, equal to, or more than 10 cm? Justify your answer.

Answer. (a) focal length
OR
half the radius of curvature

(b) 1 mark for each point:
- The inversion will happen at a distance less than 10 cm.
- A thicker lens has a smaller focal length.

Q: 13 A person needs a lens of power -5.0 D for correction of his vision.

(a) What is the possible vision defect of the person?
(b) What is the focal length of the corrective lens?

Answer. (a) myopia

(b) 0.5 marks each for correct value and unit: -0.2 m

Q: 14 A lens made of material with refractive index 1.5 is immersed in a liquid with refractive index 1.5.

The diagram below shows two rays incident on the lens when it is immersed in the liquid.

Copy the diagram and draw the light rays after they pass through the lens. Justify your diagram.

Answer. 

(Students should draw the rays through the lens and further in the liquid in the same direction as the incident ray without showing any bending at the interface of the liquid and the lens.)

Since the refractive index of the liquid is equal to that of the material of the lens, the light rays do not undergo refraction as they pass from the liquid to the lens and back into the liquid.

Q: 15 The image below shows the refraction of light in three transparent rectangular blocks, X, Y and Z, made of different materials when they are placed in air. The angle of incidence is different in each case but the angle of refraction is the same in all three blocks.

Answer . speed in X > speed in Y > speed in Z

Since the angle of incidence is minimum in block X, the refractive index of material of block X is minimum.
(Award full marks even if Snell's law is not mentioned.)

The refractive index of a material is given by n = vc.
Since refractive index of block X is minimum, speed of light is maximum in block X.

OR

Since material of block X is the least dense, the speed of light is maximum in block X.

Since refractive index of block X is minimum, speed of light is maximum in block X.
OR
Since material of block X is the least dense, the speed of light is maximum in block X.

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