Class 7 – Light (Practice Question)
Section 1
Q1. Briefly mention what makes things visible to us.
Answer:
Objects are visible to us when light falls on them and is reflected into our eyes. Without light, we cannot see anything.
Q2. Explain why concave mirror is known as a converging mirror.
Answer:
A concave mirror is called a converging mirror because it brings parallel rays of light together at a single point called the focus after reflection.
Q3. We need a shiny surface for reflection. Explain why.
Answer:
A shiny surface reflects light properly and forms a clear image. Rough surfaces scatter light in different directions and do not form clear reflections.
Q4. Differentiate between a plane mirror, concave mirror and a convex mirror without touching them.
Answer:
We can observe the image formed:
- A plane mirror forms an image of the same size.
- A concave mirror may form enlarged or inverted images.
- A convex mirror always forms a smaller and erect image.
Q5. Mention any two letters of English alphabet whose image formed in a plane mirror appears exactly similar to the letters.
Answer:
Examples: A, H, I, M, O (Any two)
Q6. State the characteristics of images formed by a concave mirror.
Answer:
The image formed by a concave mirror may be:
- Real or virtual
- Erect or inverted
- Enlarged, diminished or of the same size
depending on the position of the object.
Q7. It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still be able to obtain the image on the screen? Explain.
Answer:
The lens is a convex lens.
When the object is brought within the focal length of the lens, the image becomes virtual and enlarged, and it cannot be obtained on a screen.
Q8. Explain with the help of an activity that when seven colours are mixed together, white colour is formed.
Answer:
A Newton’s disc containing seven colours is rotated fast. The colours mix together and appear white, showing that white light is made up of seven colours.
Q9. If one half of a convex lens is covered with black paper, will the lens produce a complete image of the object?
Answer:
Yes, the lens will still form a complete image, but the image will be less bright because less light passes through the lens.
Q10. The image formed by a lens is always virtual, erect and smaller in size for an object kept at different positions. Identify the nature of the lens.
Answer:
The lens is a concave lens.
Section 2 (MCQs)
Q11. The object in which seven colours spread over it appears white when rotated is called:
a) Prism
b) Newton’s Disc
c) Galileo’s Disc
d) Rainbow mirror
Answer: b) Newton’s Disc
Q12. A diverging mirror is:
a) Plane mirror
b) Convex mirror
c) Concave mirror
d) All of these
Answer: b) Convex mirror
Q13. The splitting up of white light into seven colours on passing through a glass prism is called:
a) Refraction
b) Deflection
c) Dispersion
d) Scattering
Answer: c) Dispersion
Q14. A glass sphere is cut into two pieces and the inside is polished. The obtained mirror is:
a) Concave mirror
b) Plane mirror
c) Convex mirror
d) It is not a mirror
Answer: a) Concave mirror
Q15. The mirror used by doctors for examining eyes, ears, nose and throat is:
a) Real
b) Concave
c) Virtual
d) Convex
Answer: b) Concave
Q16. What is the nature of propagation of light?
a) Curvilinear
b) Rectilinear
c) Random
d) Circular
Answer: b) Rectilinear
Q17. Which of the following is a reflector of light?
a) The Sun
b) The Moon
c) Stars
d) The filament
Answer: b) The Moon
Q18. What causes the formation of shadows?
a) Rectilinear propagation of light
b) Curvilinear propagation of light
c) Total internal reflection
d) Refraction
Answer: a) Rectilinear propagation of light
Q19. A ray of light is incident on a plane mirror at an angle of incidence of 45°. What is the angle of reflection?
a) 30°
b) 45°
c) 90°
d) 0°
Answer: b) 45°
Q20. Which of the following is NOT a characteristic of a convex mirror?
a) The image lies between the pole and focus
b) The image is diminished
c) The image is erect
d) The image is real
Answer: d) The image is real
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