NCERT Solutions for Class 8 Science Chapter 10 – Light: Mirrors and Lenses

Chapter 8 of Class 8 Science explains reflection and refraction of light using mirrors and lenses. It covers image formation, ray diagrams, and applications in optical devices, helping students understand how vision and instruments work. Light is the fundamental force that allows us to perceive the world around us. In Chapter 10: Light, Mirrors, and Lenses, we delve into the fascinating mechanics of reflection and refraction. The chapter explains how images are formed by plane mirrors, concave mirrors, convex mirrors, and lenses. It also introduces ray diagrams and real-life applications of reflection and refraction, enabling students to connect theory with observation.

ALLEN provides the NCERT Solutions for Class 8 Science Chapter 10 – Light: Mirrors and Lenses to help students in solving all the textbook questions available at the end of the chapter according to the NCERT textbook. These solutions help understand the fundamental behaviour of light and how it interacts with different reflecting and refracting surfaces. This chapter introduces students to mirrors and lenses, which play an essential role in daily life and scientific instruments. This resource is useful for students in their preparation of Class 8 science exams.

1.0Download NCERT Solutions for Class 8 Science Chapter 10 Light: Mirrors and Lenses - Free PDF

Students can download the NCERT Solutions for Class 8 Science Chapter 10 PDF for effective revision and practice. The solutions are curated by ALLEN’s expert faculty members, ensuring accuracy, clarity, and complete syllabus coverage.

2.0Key Topics Covered in Class 8 Science Chapter 10

1. Laws of Reflection: Understanding that the angle of incidence is always equal to the angle of reflection (angle i = angle r).

2. Types of Mirrors:

• Plane Mirror: Forms virtual, erect images of the same size as the object.
• Convex Mirror: Curves outwards; forms virtual, erect, and diminished (smaller) images.
• Concave Mirror: Curves inwards; can form magnified images when objects are close.

3. Lenses and Refraction:

• Convex Lens: Thicker in the middle; acts as a magnifying glass.
• Concave Lens: Thinner in the middle; always forms diminished images.

4. Real-world Applications: The use of convex mirrors in vehicles and the behaviour of light passing through water in a glass tumble.

3.0NCERT Class 8 Science Chapter 10 Light: Mirrors and Lenses– Detailed Explanation

1. A light ray is incident on a mirror and gets reflected by it. The angle made by the incident ray with the normal to the mirror is 40°. What is the angle made by the reflected ray with the mirror?

(i) 40°
(ii) 50°
(iii) 45°
(iv) 60°

Solution Option (ii)

Given: ∠i = 40°

So, by the law of reflection, ∠i = ∠r = 40°

Now, the angle made by the reflected ray with the mirror
= 90° − 40° = 50°

2. Fig. 10.22 shows three different situations where a light ray falls on a mirror:

(i) The light ray falls along the normal
(ii) The mirror is tilted, but the light ray still falls along the normal to the tilted surface.
(iii) The mirror is tilted, and the light ray falls at an angle of 20° from the normal.

Draw the reflected ray in each case (Use a ruler and protractor for accurate drawing). What is the angle of reflection in each case?

Solution
(i)  

(ii)

(iii)

3. In figure, the cap of a sketch pen is placed in front of three types of mirrors.

Match each image with the correct mirror.

Solution

Image	Mirror	Image	Reason
(i)	Plane mirror		A plane mirror forms a virtual, erect, and the same size image of the object.
(ii)	Convex mirror		A convex mirror forms a virtual, erect, and diminished image of the object
(iii)	Concave mirror		A concave mirror forms a virtual, erect, and magnified image of the object

4. In figure the cap of a sketch pen is placed behind a convex lens, a concave lens, and a flat transparent glass piece — all at the same distance. Match each image with the correct type of lens or glass.

Solution:

Image	Lens/Glass Type	Image	Reason
(i)	Flat transparent glass piece		A flat transparent glass piece creates an image that is the same size as the object.
(ii)	Convex lens		A convex lens forms a virtual, erect, and magnified image of an object
(iii)	Concave lens		A concave lens forms a virtual, erect, and diminished image of the object.

5. When the light is incident along the normal on the mirror, which of the following statements is true?

(i) Angle of incidence is 90°
(ii) Angle of incidence is 0°
(iii) Angle of reflection is 90°
(iv) No reflection of light takes place in this case

Solution: Option (ii) When light is incident along the normal on a mirror, both the angle of incidence and the angle of reflection are 0°.

6. Three mirrors — plane, concave, and convex — are placed in Figure. On the basis of the images of the graph sheet formed in the mirrors, identify the mirrors and write their names above the mirrors.

Image	Given Image	Mirror type	Reason
(i)		Convex mirror	The grid lines seen through this lens are magnified, meaning the squares appear larger than the actual grid squares in the background. The lines also appear to bulge outwards from the center.
(ii)		Plane mirror	The grid lines reflected in it are not distorted, magnified, or reduced in size. The reflected squares are the same size as the background grid squares.
(iii)		Concave mirror	The grid lines seen through this lens are minified, meaning the squares appear smaller than the actual grid squares. The lines appear to curve inwards toward the center.

7. In a museum, a woman walks towards a large convex mirror (Fig. 10.26). She will see that:

(i) her erect image keeps decreasing in size.
(ii) her inverted image keeps decreasing in size.
(iii) her inverted image keeps increasing in size, and eventually it becomes erect and magnified.
(iv) her erect image keeps increasing in size.

Solution: Option (iv)

She will see that her reflection is upright, virtual, and smaller than she is.  As she continues to walk towards the mirror, her diminished reflection will appear to get larger, but it will always remain smaller than her actual size.

8. Hold a magnifying glass over the text and identify the distance at which you can see the text bigger than they are written. Now move it away from the text. What do you notice? Which type of lens is a magnifying glass?

Solution: When you hold a magnifying glass close to the text and slowly move it up and down, you’ll notice that at a certain distance the letters appear bigger than their actual size. If you move the lens farther away, the letters become blurred or even appear inverted (upside down) depending on how far you go. This happens because a magnifying glass is a convex lens.

9. Match the entries in Column I with those in Column II.

10. The following question is based on Assertion/Reason.

Assertion: Convex mirrors are preferred for observing the traffic behind us.
Reason: Convex mirrors provide a significantly larger view area than plane mirrors.

Choose the correct option:

(i) Both Assertion and Reason are correct, and Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are correct, but Reason is not the correct explanation for Assertion.
(iii) Assertion is correct, but Reason is incorrect.
(iv) Both Assertion and Reason are incorrect.

Solution: Option (i)

A convex mirror is curved outwards. Due to its shape, it spreads the light rays and reveals a wider area than a plane mirror. That’s why we can see more of the road and vehicles behind us. This makes driving safer.

So, convex mirrors are used as rear-view mirrors in vehicles, since they give a larger field of view even though the image looks smaller.

11. In Fig. 10.27, note that O stands for object, M for mirror, and I for image.

Which of the following statements is true?

(i) Figure (a) indicates a plane mirror, and Figure (b) indicates a concave mirror.
(ii) Figure (a) indicates a convex mirror and Figure (b) indicates a concave mirror.
(iii) Figure (a) indicates a concave mirror and Figure (b) indicates a convex mirror.
(iv) Figure (a) indicates a plane mirror, and Figure (b) indicates a convex mirror.

Solution: Option (ii)

Figure (i) shows an erect, small image which can be formed only by a convex mirror.
Figure (ii) shows an erect, large image which can be formed only by a concave mirror when the object is very close to the mirror.
In both figures, a plane mirror cannot be used because it always forms an erect image of the same size as the object.

12. Place a pencil behind a transparent glass tumbler (Fig. 10.28a). Now fill the tumbler halfway with water (Fig. 10.28b).  How does the pencil appear when viewed through the water?  Explain why its shape appears changed.

Solution

In figure (a), when you place a pencil behind an empty transparent glass tumbler, it looks normal.

In figure (b), when the tumbler is filled halfway with water and viewed through it, the part of the pencil that is under the water looks magnified or thicker.

This is because the part of the tumbler filled with water behaves like a convex lens.

4.0Key Features and Benefits of Class 8 Science Chapter 10

• Simplifies Image Formation Concepts: Clearly explains how mirrors and lenses form images using easy-to-understand ray diagrams.
• Structured Step-by-Step Answers: Provides logical solutions that help students approach numerical and diagram-based questions confidently.
• Focus on Ray Diagram Interpretation: Enhances understanding of reflection and refraction through visual explanations.
• Real-Life Applications Covered: Connects concepts to devices like mirrors, lenses, periscopes, and optical instruments.
• Strengthens Concept Accuracy: Helps differentiate between real and virtual images, focal length, and types of lenses.
• Improves Problem-Solving Skills: Guides students in solving application-based and conceptual questions effectively.
• Exam-Oriented Clarity: Highlights key concepts and frequently asked questions for better scoring in exams.