Light Mirrors and Lenses Class 8 Question Answer Science Chapter 10

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Class 8 Science Curiosity Chapter 10 Question Answer

Class 8 Science Ch 10 Light Mirrors and Lenses Question Answer

Class 8 Science Chapter 10 Light Mirrors and Lenses Question Answer (InText)

Question 1.
Can we make mirrors which can give enlarged or diminished image? (Page 152)
Answer:
Yes, concave mirrors can show bigger images and convex mirrors show smaller images, depending on how far object is.

Question 2.
Why is there a curved line on some reading glasses? (Page 152)
Answer:
The curved line shows that the glasses have two parts to see clearly both near and far.

Question 3.
How can we distinguish between concave and convex mirrors? (Page 155)
Answer:

Feature	Concave mirror	Convex mirror
Shape	Curves inward like a cave	Bulges outward
Image formed	Can be big or inverted (real/virtual)	Always small and upright (virtual)
Common use	Used in shaving or dentist mirrors	Used in vehicle rear view mirror

Question 4.
How can you identify whether a mirror is plane, concave or convex just by looking at the images formed in it? (Page 156)
Answer:
We can identify the type of mirror by looking at the image it forms. A plane mirror shows an image that is the same size and upright. A concave mirror shows a bigger image when the object is close and an inverted image when far. A convex mirror always shows a smaller, upright image.

Question 5.
Where do we find concave and convex mirrors being used in our surrounding? (Page 156)
Answer:
We see concave mirrors in shaving mirrors, dentist tools, and headlights to focus light. Convex mirrors are used in vehicle rearview mirrors, security mirrors in shops and on blind turns to see a wider view.

Question 6.
Are there any laws that govern image formation in different type of mirrors? (Page 157)
Answer:
Yes, image formation in mirrors follows the laws of reflection. These laws apply to all mirrors—plane, concave and convex for forming images.

Question 7.
Are laws of reflections applicable to spherical mirrors also? (Page 160)
Answer:
Yes, the laws of reflection are also applicable to spherical mirrors like concave and convex mirrors.

Question 8.
What is the difference in the way a concave mirror and a convex mirror affect a light beam? (Page 161)
Answer:
A concave mirror converges (brings together) a light beam to a point, while a convex mirror diverges (spreads out) the light beam.

Question 9.
Why does the light get concentrated in a small area when a concave mirror converges it? (Page 161)
Answer:
A concave mirror reflects light rays inward toward a single point called the focus, so the light gets concentrated in a small area.

Question 10.
How do object look when viewed through transparent materials with curves surfaces? (Page 162)
Answer:
When we look through transparent materials with curved surfaces, objects may look bigger, smaller, bent, or distorted depending on the shape of the surface.

Question 11.
What changes can be seen in the objects when viewed through lenses? (Page 163)
Answer:
When we look through lenses, objects may appear bigger, smaller, closer, or farther depending on the type of lens used.

Question 12.
Do lenses also converge or diverge the light beam? (Page 163)
Answer:
Yes, lenses can converge or diverge light. A convex lens converges (brings together) light rays, while a concave lens diverges (spreads out) light rays.

Question 13.
Convex lens converges a light beam, can it also burn a paper? (Page 164)
Answer:
Yes, a convex lens can burn paper by focusing sunlight to a single point, which produces enough heat to ignite it.

Question 14.
Where all are the lenses used? (Page 165)
Answer:
Lenses are used in spectacles, microscopes, magnifying glasses, cameras, telescopes, and projectors to see clearly or enlarge images.

Light Mirrors and Lenses Class 8 Questions and Answers (Exercise)

Question 1.
A light ray is incident on a mirror and gets reflected by it (See figure). 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?

Answer:
Given
Angle of incident = 40 (angle between the incident ray and the normal)
By the law of reflection,
Angle of incidence = Angle of reflection = 40°
The reflected ray makes an angle of 40° with the normal too.
So, angle made by the reflected ray with the mirror = 90°- 40°= 50°

Question 2.
Given figures show 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 reflected in each case?

Answer:
(i) Angle of incidence = 0°
Hence, angle of reflection = 0°
Reflected ray will go back along the same path.

(ii) Light is incident along the normal (even through the mirror is tilted)
So, angle of incident = 0°, hence
Angle of reflection = 0°

(iii) Angle of incidence = 20°
By law of reflection,
Angle of reflection =20°

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

Answer:
(i) The image is same size and upright → This is a plane mirror
(ii) The image appears enlarged and upright → This is a concave mirror
(iii) The image is smaller and upright → This is a concave mirror.

Question 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.

Answer:

Question 5.
When the light is incident along the normal on the mirror, which of the following statements is true?
(a) Angle of incidence is 90°
(b) Angle of incidence is 0°
(c) Angle of reflection is 90°
(d) No reflection of light takes place in this case
Answer:
The statement (b) is correct. Angle of incidence is 0° because when a light ray falls along the normal it meets the mirror at zero degrees and is reflected at the same angle.

Question 6.
Three mirrors-plane, concave and convex are placed in given figure. On the basis of the image of the graph sheet formed in the mirrors, identify the mirrors and write their names above the mirrors.

Answer:

Mirror (Given fig)	Observation	Type of Mirror
(i)	Image appears same size and upright	Plane mirror
(ii)	Image is enlarged and closer	Concave mirror
(iii)	Image appears smaller and diminished	Convex mirror

Question 7.
In the museum a woman walks towards a large convex mirror (given figure). She will see that
(a) her erect image keeps decreasing in size.
(b) her inverted image keeps decreasing in size.
(c) her inverted image keeps increasing in size and eventually it becomes erect and magnified.
(d) Her erect image keeps increasing in size.

Answer:
The correct option is (d), her erect image keeps increasing in size, because a convex mirror always forms an upright virtual image that grows larger as she moves closer (though it remains smaller than the object).

Question 8.
Hold a magnifying glass over text and identify the distance where you can see the bigger than they are written. Now move it away from the text. What do you notice? Which type of lens is a magnifying glass?
Answer:
When the magnifying glass is held just a little closer to the text than its focal length, the letters appear larger and upright, as you move it farther away, the image gradually shrinks and becomes blurry. A magnifying glass is a convex lens.

Question 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 when 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:
(i) – (a), (ii) – (b), (iii) – (c), (iv) – (d)

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 when 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

Question 10.
Assertion (A) Convex mirrors are preferred for observing the traffic behind us.
Reason (R) Convex mirrors provide a significantly larger view area than plane mirrors.
(a) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(b) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
(c) Assertion is correct but Reason is incorrect
(d) Both Assertion and Reason are incorrect.
Answer:
(a) Both Assertion and Reason are correct and Reason is the correct explanation of Assertion, because convex mirrors give a wider field of view than plane mirrors, enabling drivers to see more traffic behind them.

Question 11.
In given figure, note that 0 stands for object, M for mirror and l for image.
Which of the following statements is true?

(a) Fig. (a) indicates a plane mirror and Fig. (b) indicates a concave mirror.
(b) Fig. (a) indicates a convex mirror and Fig. (b) indicates a concave mirror.
(c) Fig. (a) indicates a concave mirror and Fig. (b) indicates a convex mirror.
(d) Fig. (a) indicates a plane mirror and Fig. (b) indicates a convex mirror.
Answer:
The correct option is (d).In Fig. (a), the object and its upright virtual image lie at equal distances from M, which is characteristic of a plane mirror. In Fig. (b), the virtual image is closer to M than the object and is diminished, which matches a convex mirror.

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

Answer:
The pencil looks bent or “broken” at the water line because light rays change direction (refract) as they pass from water into air, making the submerged part appear shifted and distorted.

Class 8 Science Chapter 10 Question Answer (Activities)

Activity 1 (Page 153)

Aim
To observe how curved surfaces (concave and convex) form different types of images compared to a plane mirror.

Materials Required
Shiny metallic spoon, small object (e.g., a coin or key)

Procedure

1. Hold the spoon’s inner curved surface (bowl side) close to your face Fig. (a).
2. Observe the image of your face. Is it upright or inverted? Enlarged or diminished?
3. Slowly move the spoon away. Note changes in the image (e.g., flips upside down).
4. Flip the spoon to use its outer curved surface (Fig. (b).
5. Repeat observations. How does the image differ from the inner surface?
6. Place a small object (coin) near the spoon’s inner and outer surfaces.
7. Compare the images formed.

Observations

Spoon surface	Image Close-up	Image when moved away	Comparison to plane mirror
Inner (Concave)	Upright Enlarged	Inverted, Diminished	Magnifies when close
Outer (Convex)	Upright, Diminished	Remains small and upright	Always reduces image size.

Conclusion

1. The spoon’s inner surface acts like a concave mirror, forming both enlarged and inverted images depending on distance.
2. The outer surface behaves like a convex mirror, always producing smaller, upright images.
3. Unlike a plane mirror, curved surfaces distort image size and orientation.

Viva Questions

1. Why does your reflection flip upside down when you move the spoon’s inner surface away?
2. How is the outer spoon surface useful in real life?
3. What happens if you use a non-shiny spoon? Why?

Activity 2 (Page 155)

Aim
To distinguish between concave and convex mirrors by observing their curved surfaces.

Materials Required
Concave mirror, convex mirror, flat surface (table)

Procedure

1. Keep both mirrors on a table with their reflecting surfaces facing upward.
2. Bend down to bring your eyes to the same level as the mirrors (See figure).
3. Observe the curvature of each mirror’s reflecting surface from the side.
4. Concave Mirror The surface curves inward (like a cave).
5. Convex Mirror The surface bulges outward (like a bubble).
6. Gently run your finger along the surface (if allowed) to feel the curvature.

Observations

Mirror Type	Curvature Direction	Visual Clue
Concave	Inward	Centre appears deeper than edges
Convex	Outward	Centre bulges out, edges curve back

Conclusion

1. Concave mirrors have an inward-curved surface.
2. Convex mirrors have an outward-curved surface.
3. This difference affects how they reflect light (concave converges, convex diverges).

Viva Questions

1. How can you tell a concave mirror apart from a convex mirror just by looking?
2. Why do convex mirrors show a wider area than concave mirrors?
3. Where might you find concave mirrors in daily life?

Activity 3 (Page 155)

Aim
To observe and compare the images formed by a concave and a convex mirror at different distances of an object.

Materials Required
1 concave mirror, 1 convex mirror, 2 small wooden blocks or stands, a small toy or object (e.g., candle or pencil), a table or flat surface, ruler or measuring scale.

Procedure

• Fix the concave mirror and the convex mirror vertically on wooden blocks.
• Place them side by side on a table.
• Keep a small object (like a toy) 3 – 4 cm in front of both mirrors.
• Observe the images formed in both mirrors: Note the size, nature, orientation, and lateral inversion of the image.
• Move the object gradually away from the mirrors.

• For each distance, observe
  Is the image getting larger or smaller?
  Is the image erect or inverted?
  Is the image virtual or real (if visible on screen)?
• Repeat the above steps for each mirror individually

Observations

Mirror Type	At small distance (3 – 4 cm)	At Large distance
Concave	Erect, larger and virtual image	Inverted, smaller/real image
Convex	Erect, diminished and virtual image	Erect, more diminished, virtual image

Conclusion

1. Concave Mirror forms
   a. Virtual, erect and enlarged image when the object is close.
   b. Real, inverted and smaller image when the object is far.
2. Convex Mirror always forms
   a. Virtual, erect, and diminished image regardless of the object’s distance.

Viva Questions

1. What type of image is formed by a concave mirror when the object is close?
2. Why is the image in a convex mirror always diminished?
3. Why do you think barbers prefer using a specific type of mirror while cutting hair or shaving?

Activity 4 (Page 157)

Aim
To verify the laws of reflection using a plane mirror.

Material Required
Plane mirror with stand, torch, comb, paper clip (to hold the comb.

Procedure

1. Cover a comb with black paper, leaving only the middle slit open.
2. Shine a torch through the slit to create a thin light beam on white paper.
3. Place a plane mirror upright on the paper.
4. Direct the light beam at the mirror Fig. (a).
5. Adjust the angle and note how the reflected beam shifts Fig. (b).
6. Mark the incident ray, reflected ray, and normal (perpendicular line).
7. Measure angles (∠i = incident, ∠r = reflected) with a protractor.

Observations

Angle of Incidence (∠i)	Angle of Reflection (∠r)	Remarks
30°	30°	∠i = ∠r
45°	45°	∠i = ∠r
60°	60°	∠i = ∠r

Conclusion
The experiment verifies the two laws of reflection

1. ∠i = ∠r.
2. All rays lie in the same plane.

Viva Questions

1. What kind of image is formed by a plane mirror?
2. Does the image formed in a plane mirror show lateral inversion?
3. If the incident ray is at 30°, what will be the angle of reflection?

Activity 5 (Page 159)

Aim
To demonstrate that the incident ray, normal and reflected ray lie in the same plane (2nd law of reflection).

Materials Required
Plane mirror with stand, torch, comb (with middle slit open), stiff chart paper, pencil.

Procedure

1. Place the chart paper flat on a table, with part extending beyond the edge.
2. Position the plane mirror upright on the paper.
3. Shine a thin beam of light (using the comb and torch) onto the mirror [Fig. (a)].
4. Trace the incident ray and reflected ray on the extended paper.
5. Gently bend the extended portion downward along the table’s edge [Fig. (b)].
6. Observe if the reflected ray is still visible on the bent part.
7. Flatten the paper again and check if the reflected ray reappears.

Observation

1. When the paper is flat, the reflected ray is clearly visible on the extended portion.
2. When the paper is bent, the reflected ray disappears from view.
3. Upon straightening the paper, the reflected ray becomes visible again.

Conclusion
This demonstrates that the incident ray, normal and reflected ray must all lie in the same plane. When we bend the paper, we change the plane, causing the reflected ray to no longer align With our viewing surface.

Activity 6 (Page 160)

Aim
To study how plane, concave and convex mirrors reflect multiple parallel beams of light and understand their unique properties.

Materials required
Plane mirror, concave mirror, convex mirror, mirror stand, torch, comb (with multiple slits uncovered), white paper sheet, black paper strips.

Procedure

1. Cover the comb with black paper, leaving multiple slits open to create parallel beams of light.
2. Shine the torch through the comb to project multiple parallel beams onto a white paper sheet.
3. Place the mirror in the path of the beams. Observe and sketch the reflected beams [Fig. (b)].
4. Replace with the concave mirror. Note if the reflected beams converge [Fig. (c)].
5. Repeat with the convex mirror. Observe if the beams diverge [Fig. (d)].
6. Record differences in beam behavior for each mirror type.

Observation Table
Reflection from Different Mirrors

Mirror Type	Behavior of Reflected Beams	Key Observation
Plane Mirror	Beams remain parallel	Each beam follow ∠i = ∠r independently
Concave Mirror	Beams Converge ot a point	Reflection focuses light a focal point
Convex Mirror	Beams diverge (spread out)	Reflection rays appear to come from behind.

Conclusion

1. Plane mirrors preserve parallel light beams.
2. Concave mirrors converge light due to their inward curvature (used in telescopes, headlights).
3. Convex mirrors diverge light, providing wider views (used in rear-view mirrors).

Viva Questions

1. Why do concave mirrors converge light while convex mirrors diverge it?
2. How would the results change if the light beams weren’t parallel?
3. Which mirror would be best for a solar cooker? Why?

Activity 7 (Page 161)

Aim
To demonstrate how a concave mirror converges sunlight to a focal point, producing enough heat to burn paper.

Material Required
Concave mirror, thin sheet of paper/newspaper, stand (to hold mirror steady), dark-colored paper (optional, for better observation).

Procedure

1. Perform outdoors under supervision.
2. Never look at the Sun or mirror directly.
3. Face concave mirror toward the Sun.
4. Hold paper in front; adjust distance to form a sharp bright spot (focal point).
5. Hold steady for 2 – 3 minutes.
6. Observe if spot burns/smokes.
7. Repeat with plane mirror (no spot forms).

Observations

Mirror type	Bright spot Formed	Heating effect	Reason
Concae mirror	Yes	Paper burns/smokes	Sunlight converges at focal point
Plane mirror	No	No effect	Reflects light without convergence.

Conclusion
The concave mirror’s curved surface focuses parallel sunlight to a single point, generating intense heat that can ignite paper. This verifies its converging proeperty.

Viva Questions

1. Why doesn’t a plane mirror burn paper?
2. What factors affect the experiment’s success?
3. How is this principle used in solar cookers?

Activity 8 (Page 162)

Aim
To demonstrate how a water droplet acts as a convex lens and magnifies text.

Materials Required
Glass/plastic strip, oil/wax, water dropper, printed text (book/newspaper).

Procedure

1. Apply oil/wax on the strip and rub to form a thin coating.
2. Place a water droplet on the coated area (forms a curved surface).
3. Position printed text beneath the strip.
4. View text through the water drop.
   Note if letters appear enlarged.
5. Observe text without the droplet for comparison.

Observations

1. Water droplet surface curves outward (convex shape).
2. Text beneath droplet appears larger (magnified).
3. Without droplet, text appears normal.

Conclusion
The curved water droplet acts as a convex lens, converging light to magnify objects. This mimics how magnifying glasses work.

Viva Questions

1. What is the shape of the water droplet formed on the oiled surface?
2. Why does the text appear enlarged when viewed through the water drop?
3. What happens if we use a larger water droplet?

Activity 9 (Page 163)

Aim
To study how convex and concave lenses form images of an object at different distances.

Materials Required
Convex lens, concave lens, lens holder/stand, small object (e.g., a pin or printed text), Measuring scale (optional).

Procedure
Part A: Convex Lens

1. Mount the convex lens vertically using the holder.
2. Place the object close to the lens (within focal length).
3. View the object through the lens Fig. (a).
4. Note the image nature (erect/enlarged).
5. Gradually move the object away from the lens.
6. Observe changes in the image (inversion, size reduction).

Part B : Concave Lens

1. Replace the convex lens with a concave lens.
2. Observe the image at different distances (always erect/diminished).

Observations

Lens type	Object position	Image appearance
Thick-Centre	Very close to lens	Upright and bigger
	Moderately far from lens	Upside down and bigger
	Vergy far from lens	Upside down and smaller
Thin-Centre	Any distance	Always upright and smaller

Conclusion

1. Convex lenses can form real or virtual images depending on object distance.
2. Concave lenses always form virtual, diminished images.

Viva Questions

1. Why does the thick-centre lens flip the image when the object moves far away?
2. Can the thin-centre lens ever make an image look bigger? Why?
3. How could you use a thick-centre lens to read tiny text?

Activity 10 (Page 164)

Aim
To observe how light behaves when passing through a flat glass plate, a converging lens (convex) and a diverging lens (concave).

Materials Required
Thin transparent glass plate, convex lens (converging lens), concave lens (diverging lens), torch, comb (to create parallel light beams), paper clip (to hold the comb upright), two identical books, white paper sheets.

Procedure
Use the comb to create multiple parallel beams of light by shining the torch through its slits.

1. Secure the comb upright with a paper clip.
2. Place two books side by side to create a stable stand.
3. Lay white paper sheets on the books to observe the light beams clearly.
4. Place the glass plate vertically between the books.
5. Direct the parallel light beams through it [Fig. (a)].
6. Observe and record if the beams remain parallel.
7. Replace the glass plate with the convex lens [Fig. (b)].
8. Observe if the beams converge (come together) after passing through.
9. Replace the convex lens with the concave lens [Fig. (c)].
10. Observe if the beams diverge (spread out) after passing through.
11. Note the behaviour of light beams for each material

Observations

Material	Behaviour of Light beams	Key observation
Thin Glass Plate	Beams ramain parallel	Light passes through without bending
Convex Lens	Beams converge (come together)	Light bends inward, focusing at a point.
Concave lens	Beams diverge (spread out)	Light bends outward, appearing to spread.

Conclusion

1. Flat surfaces (like glass plates) do not alter the path of parallel light beams.
2. Convex lenses bend light inward, making beams converge.
3. Concave lenses bend light outward, making beams diverge.

Viva Questions

1. Why does the glass plate not change the direction of the light beams?
2. How does the convex lens help in focusing light?
3. What happens if you use a thicker glass plate instead of a thin one?
4. Can a concave lens ever make light beams converge? Why or why not?

Activity 11 (Page 165)

Aim
To show how a thick-centre lens brings sunlight together to create heat.

Materials Required
Thick-centre lens (like a magnifying glass), dark paper, stand (optional).

Procedure

1. Do this outside with an adult.
2. Never look at the Sun or through the lens.
3. Hold the lens facing the Sun.
4. Move it up/down until sunlight makes a tiny bright dot on the paper.
5. Keep still for 1 minute.
6. Does the dot get hot and burn the paper?

Observation

1. When sunlight passes through the thick-centre lens, it forms a tiny, bright dot on the paper.
2. After holding the lens steady for 1 – 2 minutes, the dot smokes or burns the paper.
3. No burning occurs if
   (a) The lens is too high/low (no sharp dot forms).
   (b) A thin-centre lens is used (light spreads out instead).

Conclusion

1. The thick-centre lens bends sunlight inward, concentrating it into a small spot. This focused light produces enough heat to burn the paper. It demonstrating how such lenses:
2. Work in magnifying glasses (to enlarge objects)
3. Help eyeglasses correct vision
4. Are used in cameras to focus light

Viva Questions

1. Why does the bright dot appear on the paper?
2. What would happen if you used a drop of water as a lens instead?
3. Why is it dangerous to look at the Sun through this lens?