Light: Mirrors And Lenses Class 8 Science Curiosity Chapter 10 Questions Answers If you are searching for Light: Mirrors And Lenses Class 8 Science Curiosity Chapter 10 Questions Answers, you’ve come to the right place. This chapter helps students understand the concepts of reflection, mirrors, lenses, image formation, and their applications in everyday life. These solutions are written in simple language so that students can prepare effectively for school exams and strengthen their understanding of the chapter.
Probe and ponder (Page 152)
Q. Can we make mirrors which can give enlarged or diminished images?
Answer:
Yes, we can make mirrors that give enlarged or diminished images. Such mirrors are called spherical mirrors.
A concave mirror, whose reflecting surface curves inward, can form enlarged images of objects.
A convex mirror, whose reflecting surface curves outward, always forms diminished images of objects.
Q. 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:
The side-view mirrors of vehicles are convex mirrors. Convex mirrors make the images of objects smaller and appear farther away than they actually are.
Therefore, the warning “Objects in the mirror are closer than they appear” is written to remind drivers that the vehicles seen in the mirror are actually closer than they seem.
Q. Why is there a curved line on some reading glasses?
Answer:
The curved line on some reading glasses is due to the presence of bifocal lenses. This line separates the two parts of the lens that have different focal lengths.
The upper part of the lens is used for distant vision, while the lower part is used for reading or near vision.
Keep the curiosity alive (Page 166)
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°
Answer:
Given,
∠i = 40°
According to the law of reflection,
∠i = ∠r = 40°
The angle made by the reflected ray with the mirror = 90° − ∠r
= 90° − 40°
= 50°
Hence, the correct answer is (ii) 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?
Answer:
(i) The light ray falls along the normal.
The angle of incidence (∠i) = 0°
Therefore, according to the law of reflection,
The angle of reflection (∠r) = 0°
(ii) The mirror is tilted, but the light ray still falls along the normal to the tilted surface.
The angle of incidence (∠i) = 0°
Therefore, according to the law of reflection,
The angle of reflection (∠r) = 0°
(iii) The mirror is tilted, and the light ray falls at an angle of 20° from the normal.
The angle of incidence (∠i) = 20°
Therefore, according to the law of reflection,
The angle of reflection (∠r) = 20°
3. In Fig. 10.23, the cap of a sketch pen is placed in front of three types of mirrors.
Match each image with the correct mirror.
Answer:
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.
Answer:
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
Answer:
(ii) Angle of incidence is 0°
Explanation:
When light is incident along the normal, it means the light ray falls perpendicularly on the mirror.
Hence, the angle between the incident ray and the normal is 0°.
The reflected ray also goes back along the same path, as the angle of reflection is also 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:
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.
Answer:
A convex mirror always forms an erect and diminished image of the object, no matter how far the object is. Hence, option (i) is correct.
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?
Answer:
When we hold a magnifying glass over the text, the letters appear larger and clearer. As we move the lens away from the text, the letters first become bigger and then blurred, and finally appear inverted and smaller when the lens is moved farther away. This shows that a magnifying glass is a convex lens.
9. Match the entries in Column I with those in Column II.
Answer:
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.
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.
Answer:
(i) Figure (a) indicates a plane mirror and Figure (b) indicates a concave 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:
When the tumbler is empty (Fig. 10.28 a), the pencil appears straight. But when the tumbler is half-filled with water (Fig. 10.28 b), the pencil appears bent or broken at the surface of water.
This happens because of refraction of light. Light rays coming from the part of the pencil inside water bend when they pass from water to air. Due to this bending of light, the submerged part of the pencil seems to be at a different position, making the pencil appear displaced or bent at the surface.
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