Class 8 Science Chapter 10 – Light: Mirrors and Lenses from NCERT Curiosity with easy Notes and complete Book Solutions. Get simple explanations, important concepts, questions and answers, and revision material for effective learning, practice and exam preparation.
Chapter 10 – Light: Mirrors and Lenses
Curiosity — Textbook of Science for Grade 8
Probe and ponder
Can we make mirrors which can give enlarged or diminished images?
Answer: Yes. Concave and convex mirrors can give enlarged or diminished images depending on the position of the object.
On side-view mirrors of vehicles, there is a warning that says “Objects in mirror are closer than they appear”. Why is this warning written there?
Answer: Side-view mirrors are convex mirrors. They make objects appear smaller and farther away than they actually are.
Why is there a curved line on some reading glasses?
Answer: The curved line may indicate a change in the lens surface or a special lens design used for different viewing distances.
Share your questions
Think: Write any question you have about mirrors, lenses, images, reflection or light.
10.1 What Are Spherical Mirrors?
Easy Concept
Spherical mirror: A mirror whose reflecting surface is spherical is called a spherical mirror.
Concave mirror: A spherical mirror whose reflecting surface curves inwards.
Convex mirror: A spherical mirror whose reflecting surface curves outwards.
Easy way to remember:
Concave → curves inward.
Convex → bulges outward.
Concave → curves inward.
Convex → bulges outward.
Activity 10.1: Let us explore
- Take a shiny metallic spoon and look at its curved surface.
- The inner side behaves like a concave mirror.
- The outer side behaves like a convex mirror.
- The inner side can form an inverted image when the face is sufficiently far away.
- The outer side forms an erect and smaller image.
Remember: A concave mirror curves inward, while a convex mirror curves outward.
Activity 10.2: Let us distinguish
Concave and convex mirrors can be distinguished by looking at the direction in which their reflecting surfaces curve.
Concave
Curves inward → )
Convex
Bulges outward → (
Curves inward → )
Convex
Bulges outward → (
10.2 What Are the Characteristics of Images Formed by Spherical Mirrors?
Activity 10.3: Let us explore
Concave mirror: When the object is close, the image can be erect and enlarged. When the object is moved farther away, the image becomes inverted and its size can decrease.
Convex mirror: The image is always erect and smaller than the object.
Plane mirror: The image is always erect and of the same size as the object.
Lateral inversion: The left and right sides appear interchanged in the image.
Uses of Concave Mirrors
- Reflectors of torches.
- Headlights of cars and scooters.
- Dental mirrors.
- Reflecting telescopes.
- Solar concentrators.
Uses of Convex Mirrors
- Side-view mirrors of vehicles.
- Road safety mirrors at bends and intersections.
- Surveillance mirrors in large stores.
Why are convex mirrors used in vehicles?
They form erect, diminished images and provide a wider field of view.
They form erect, diminished images and provide a wider field of view.
10.3 What Are the Laws of Reflection?
Activity 10.4: Let us experiment
Incident ray: The ray of light that falls on the mirror.
Reflected ray: The ray of light that comes back from the mirror.
Normal: An imaginary line perpendicular to the mirror at the point where the ray strikes it.
Angle of incidence: The angle between the incident ray and the normal.
Angle of reflection: The angle between the reflected ray and the normal.
Angle of incidence = Angle of reflection
i = r
i = r
Two Laws of Reflection
- The angle of incidence is equal to the angle of reflection.
- The incident ray, the normal to the mirror at the point of incidence, and the reflected ray all lie in the same plane.
Special case: When a light ray falls along the normal, both the angle of incidence and angle of reflection are 0°.
Activity 10.5: Let us experiment
The activity shows that the incident ray, normal and reflected ray remain in the same plane.
Activity 10.6: Let us explore
| Mirror | Effect on parallel rays |
|---|---|
| Plane mirror | Reflected rays remain parallel. |
| Concave mirror | Rays converge. |
| Convex mirror | Rays diverge. |
Activity 10.7: Let us explore
Safety: Never look directly at the Sun or at sunlight reflected by a mirror. The concentrated sunlight can damage the eyes and can burn paper.
A concave mirror can concentrate sunlight at a small bright spot. The concentrated light produces heat and can ignite paper.
Solar concentrators: Devices that use mirrors or lenses to concentrate sunlight into a small area.
10.4 What Is a Lens?
Easy Concept
Lens: A piece of transparent material, usually glass or plastic, having curved surfaces.
Convex lens: Thicker at the middle and thinner at the edges.
Concave lens: Thinner at the middle and thicker at the edges.
Easy way to remember:
Convex lens → thick in the centre.
Concave lens → thin in the centre.
Convex lens → thick in the centre.
Concave lens → thin in the centre.
Activity 10.8: Let us explore
A curved water drop can act like a simple lens. It can make the letters underneath appear larger.
A magnifying glass uses a convex lens to make small print appear larger when the object is at a suitable distance.
Activity 10.9: Let us experiment
| Lens | Image formed |
|---|---|
| Convex lens | Can be erect/enlarged when close; can become inverted and smaller as distance increases. |
| Concave lens | Always erect and diminished. |
Activity 10.10: Let us investigate
| Material | Effect on parallel light |
|---|---|
| Thin glass plate | Light passes through almost as it is. |
| Convex lens | Converges the light. |
| Concave lens | Diverges the light. |
Convex lens = Converging lens
Concave lens = Diverging lens
Concave lens = Diverging lens
Activity 10.11: Let us investigate
Do not look at the Sun directly or through a lens. Concentrated sunlight can damage your eyes.
A convex lens can concentrate sunlight on a small area and produce enough heat to burn paper.
Where are lenses used?
- Eyeglasses.
- Cameras.
- Telescopes.
- Microscopes.
- Human eye.
- Magnifying glasses.
Snapshots – Quick Revision
1. Image formed by a concave mirror can be enlarged, diminished or of the same size as the object, and it may be erect or inverted, depending upon the distance of the object from the mirror.
2. Image formed by a convex mirror is always erect and diminished in size.
3. The angle of incidence is equal to the angle of reflection.
4. The incident ray, normal and reflected ray lie in the same plane.
5. The laws of reflection are valid for plane, concave and convex mirrors.
6. A concave mirror converges light beams while a convex mirror diverges them.
7. A convex lens can form enlarged, diminished or same-size images depending on the object distance.
8. A concave lens always forms an erect and diminished image.
9. A convex lens converges light beams while a concave lens diverges them.
Keep the curiosity alive
1. A light ray is incident on a mirror and gets reflected by it (Fig. 10.21). 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°
(i) 40° (ii) 50° (iii) 45° (iv) 60°
Answer: (ii) 50°
Angle of incidence = 40°.
Angle of reflection = 40°.
Therefore, angle made by reflected ray with the mirror = 90° − 40° = 50°.
Angle of incidence = 40°.
Angle of reflection = 40°.
Therefore, angle made by 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?
(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?
Answer:
(i) Angle of reflection = 0°.
(ii) Angle of reflection = 0°.
(iii) Angle of reflection = 20°.
In each case, draw the reflected ray so that it makes the same angle with the normal as the incident ray.
(i) Angle of reflection = 0°.
(ii) Angle of reflection = 0°.
(iii) Angle of reflection = 20°.
In each case, draw the reflected ray so that it makes the same angle with the normal as the incident ray.
3. In Fig. 10.23, the cap of a sketch pen is placed in front of three types of mirrors.
Answer: Match the images using these properties:
- Same-size image → Plane mirror.
- Erect and diminished image → Convex mirror.
- Enlarged/inverted image depending on position → Concave mirror.
| Image | Mirror |
|---|---|
| (i) | Plane mirror |
| (ii) | Convex mirror |
| (iii) | Concave mirror |
4. In Fig. 10.24, 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.
Image Lens/glass type
(i) Flat transparent glass piece
(ii) Convex lens
(iii) Concave lens
Match each image with the correct type of lens or glass.
Image Lens/glass type
(i) Flat transparent glass piece
(ii) Convex lens
(iii) Concave lens
Answer:
The flat glass piece produces little or no size change.
A convex lens can produce an enlarged image when the object is close.
A concave lens produces an erect and diminished image.
The flat glass piece produces little or no size change.
A convex lens can produce an enlarged image when the object is close.
A concave lens produces an erect and diminished image.
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
(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
Answer: (ii) Angle of incidence is 0°.
6. Three mirrors—plane, concave and convex are placed in Fig. 10.25. On the basis of the images of the graph sheet formed in the mirrors, identify the mirrors and write their names above the mirrors.
Answer: Identify them by the image:
- Same-size image → Plane mirror.
- Erect, smaller image → Convex mirror.
- Enlarged or inverted image depending on position → Concave mirror.
7. In a museum, a woman walks towards a large concave 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.
(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.
Answer: (iii) her inverted image keeps increasing in size and eventually it becomes erect and magnified.
8. Hold a magnifying glass over text and identify the distance where 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?
(i) (ii) (iii)
(i) (ii) (iii)
Answer: At a suitable small distance, the letters appear enlarged and erect. When the magnifying glass is moved away, the appearance changes and the letters may become smaller or inverted. A magnifying glass uses a convex lens.
9. Match the entries in Column I with those in Column II.
Column I Column II
(i) Concave mirror (a) Spherical mirror with a reflecting surface that curves inwards.
(ii) Convex mirror (b) It forms an image which is always erect and diminished in size.
(iii) Convex lens (c) Object placed behind it may appear inverted at some distance.
(iv) Concave lens (d) Object placed behind it always appears diminished in size.
Column I Column II
(i) Concave mirror (a) Spherical mirror with a reflecting surface that curves inwards.
(ii) Convex mirror (b) It forms an image which is always erect and diminished in size.
(iii) Convex lens (c) Object placed behind it may appear inverted at some distance.
(iv) Concave lens (d) Object placed behind it always appears diminished in size.
Answer:
| Column I | Correct Column II |
|---|---|
| (i) Concave mirror | (a) |
| (ii) Convex mirror | (b) |
| (iii) Convex lens | (c) |
| (iv) Concave lens | (d) |
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.
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.
Answer: (i) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
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.
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.
Answer: (iii) Figure (a) indicates a concave mirror and Figure (b) indicates a convex mirror.
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.
Answer: The pencil may appear bent, displaced or changed in shape when viewed through the water. This happens because light changes its direction when it passes from one transparent medium to another. This effect is called refraction of light.
Think More
Why?
Think about why mirrors and lenses form different images.
When?
Think about when a concave mirror or convex lens forms an enlarged image.
How long?
Write your own science question related to the time taken by light or an experiment involving mirrors and lenses.
Where? Why not?
Think of places where mirrors or lenses are used and explain why another type would not be suitable.
Prepare some questions based on your learnings so far …
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Discover, design, and debate
Visit a nearby hospital or the clinic of an ENT specialist, or a dentist, with your teacher or parents. Request the doctor to show you the mirrors used for examining ear, nose, throat, and teeth. Identify the kind of mirror used in these instruments.
Suggested observation: Dental mirrors commonly use concave mirrors because they can provide an enlarged view when held close to the teeth. Record what the doctor actually shows you during the visit.
Harnessing sunlight is key to solving future energy challenges. In devices like solar cookers (Fig. 10.29), mirrors are used to converge sunlight and generate heat. In India, such designs are used in villages, thus saving electricity and reducing fossil fuel use. Think of a design for a solar cooker for your school or home and prepare a detailed proposal for it including the budget required.
Suggested idea: Design a solar cooker using a concave or suitably curved reflecting surface, a dark cooking container and an insulated support. The mirror should direct sunlight towards the cooking area. Include materials, estimated cost, safety measures and expected use in the proposal.
Use online tools or animation to do virtual experiments with spherical mirrors and lenses. Move objects in the simulation and observe how the image changes.
Observation: Record how image size, orientation and position change when the object is moved. Compare concave and convex mirrors and convex and concave lenses.
Our scientific heritage
More than 800 years ago, during the time of the great Indian mathematician Bhāskara II, astronomers used shallow bowls of water to observe the stars and planets.
They observed reflected images through tubes placed at appropriate angles to help measure the positions of stars and planets.
This shows that people in the past used careful observations and practical methods to study reflection and astronomy.
Reflect on the questions framed by your friends and try to answer …
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I think …
But we thought … Maybe …
Shouldn’t it be …
Quick Comparison – Mirrors and Lenses
| Device | Shape | Light effect | Image |
|---|---|---|---|
| Plane mirror | Flat reflecting surface | Reflects light | Erect and same size |
| Concave mirror | Reflecting surface curves inward | Converges light | Can be enlarged, diminished, erect or inverted |
| Convex mirror | Reflecting surface curves outward | Diverges light | Always erect and diminished |
| Convex lens | Thicker at middle | Converges light | Can be enlarged, diminished, erect or inverted |
| Concave lens | Thinner at middle | Diverges light | Always erect and diminished |
Important Words to Remember
| Term | Easy Meaning |
|---|---|
| Spherical mirror | Mirror having a spherical reflecting surface |
| Concave mirror | Curves inward |
| Convex mirror | Bulges outward |
| Incident ray | Ray falling on the mirror |
| Reflected ray | Ray coming back from the mirror |
| Normal | Line perpendicular to the mirror at the point of incidence |
| Angle of incidence | Angle between incident ray and normal |
| Angle of reflection | Angle between reflected ray and normal |
| Convex lens | Thicker in the middle |
| Concave lens | Thinner in the middle |
| Converge | Come closer together |
| Diverge | Spread apart |
| Lateral inversion | Left and right appear interchanged |
Practise Class 8 Science Chapter 10 with this easy NCERT Curiosity worksheet. Includes important questions and revision exercises to strengthen understanding, practise key concepts and prepare effectively for class tests and exams.
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