Questions for class 10th science light chapter in depth exam level questions cover all subtopics
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Here is a comprehensive set of Class 10 CBSE Science — Chapter: Light (Reflection and Refraction) exam-level questions covering all subtopics in mixed format.
🔆 Class 10 CBSE Science — Light: Reflection & Refraction
In-Depth Exam-Level Question Bank
SECTION A — Multiple Choice Questions (1 Mark each)
1. The angle of incidence is equal to the angle of reflection. This statement is:
- (a) The first law of refraction
- (b) Snell's law
- (c) The second law of reflection
- (d) The law of reversibility
2. A concave mirror produces a virtual, erect, and magnified image when the object is placed:
- (a) At infinity
- (b) At the centre of curvature
- (c) Between F and C
- (d) Between P and F ✅
3. The focal length of a concave mirror is 15 cm. Its radius of curvature is:
- (a) 7.5 cm
- (b) 15 cm
- (c) 30 cm ✅
- (d) 45 cm
4. A ray of light passing through the principal focus of a concave mirror, after reflection, will:
- (a) Pass through the centre of curvature
- (b) Travel parallel to the principal axis ✅
- (c) Pass through the pole
- (d) Retrace its path
5. Which of the following mirrors is used as a rear-view mirror in vehicles?
- (a) Plane mirror
- (b) Concave mirror
- (c) Convex mirror ✅
- (d) Both (a) and (c)
6. The refractive index of glass with respect to air is 3/2. The refractive index of air with respect to glass is:
- (a) 3/2
- (b) 2/3 ✅
- (c) 1
- (d) √(3/2)
7. A convex lens has a focal length of 20 cm. Its power is:
- (a) −5 D
- (b) +5 D ✅
- (c) +0.05 D
- (d) −0.05 D
8. An object is placed at 2F in front of a convex lens. The image formed is:
- (a) At F, diminished, real
- (b) At 2F, same size, real, inverted ✅
- (c) Beyond 2F, magnified, real
- (d) Virtual and erect
9. Light travels from a denser medium to a rarer medium. The refracted ray bends:
- (a) Towards the normal
- (b) Away from the normal ✅
- (c) Along the normal
- (d) Parallel to the surface
10. The SI unit of power of a lens is:
- (a) Metre
- (b) Centimetre
- (c) Dioptre ✅
- (d) Watt
11. For a concave mirror, magnification is negative. This means the image is:
- (a) Virtual and erect
- (b) Real and inverted ✅
- (c) Virtual and inverted
- (d) Real and erect
12. Which lens is used to correct myopia (short-sightedness)?
- (a) Convex lens
- (b) Concave lens ✅
- (c) Bifocal lens
- (d) Cylindrical lens
13. The phenomenon of bending of light around the edges of an obstacle is:
- (a) Reflection
- (b) Refraction
- (c) Diffraction ✅
- (d) Dispersion
14. If the magnification produced by a lens is +0.5, the image is:
- (a) Real, inverted, diminished
- (b) Virtual, erect, diminished ✅
- (c) Virtual, erect, magnified
- (d) Real, erect, diminished
15. A concave lens always forms an image that is:
- (a) Real and magnified
- (b) Real and diminished
- (c) Virtual, erect, and diminished ✅
- (d) Virtual and magnified
SECTION B — Assertion-Reason Questions (1 Mark each)
Choose the correct option:
- (A) Both assertion (A) and reason (R) are true, and R is the correct explanation of A.
- (B) Both A and R are true, but R is NOT the correct explanation of A.
- (C) A is true, but R is false.
- (D) A is false, but R is true.
16.
- Assertion: Convex mirrors are used as rear-view mirrors.
- Reason: Convex mirrors always form a virtual, erect, and diminished image, giving a wider field of view.
Answer: (A)
17.
- Assertion: A ray of light passing through the optical centre of a lens does not deviate.
- Reason: The two surfaces of the lens at the optical centre are parallel to each other.
Answer: (A)
18.
- Assertion: The speed of light in a vacuum is the same for all wavelengths.
- Reason: The refractive index of a vacuum is 1 for all wavelengths.
Answer: (A)
19.
- Assertion: A concave mirror can form both real and virtual images.
- Reason: The nature of image formed by a concave mirror depends on the position of the object.
Answer: (A)
20.
- Assertion: When two lenses of powers +3 D and −1 D are placed in contact, the combination acts as a converging lens.
- Reason: The net power is +2 D.
Answer: (A)
SECTION C — Short Answer Questions (2 Marks each)
21. Define the principal focus of a concave mirror. Draw a ray diagram to show the image formed when an object is placed at the centre of curvature of a concave mirror.
Answer: The principal focus (F) of a concave mirror is the point on the principal axis where rays parallel to the principal axis converge after reflection. When an object is at C (2F), the image is also formed at C — it is real, inverted, and of the same size.
22. State the two laws of reflection of light.
Answer:
- The angle of incidence is always equal to the angle of reflection (∠i = ∠r).
- The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.
23. An object 5 cm tall is placed at a distance of 30 cm from a convex lens of focal length 10 cm. Find the position and size of the image.
Using lens formula: 1/v − 1/u = 1/f u = −30 cm, f = +10 cm 1/v = 1/10 + 1/(−30) = 3/30 − 1/30 = 2/30 v = +15 cm (real, on other side) m = v/u = 15/(−30) = −0.5 Image height = −0.5 × 5 = −2.5 cm (real, inverted, diminished)
24. Why does a ray of light bend when it passes from one medium to another?
Answer: Light bends (refracts) because it travels at different speeds in different media. When it passes obliquely from a medium of one optical density to another, the change in speed causes the ray to change direction. If it enters a denser medium, it slows down and bends toward the normal; if it enters a rarer medium, it speeds up and bends away from the normal.
25. Define absolute refractive index. The speed of light in a medium is 2 × 10⁸ m/s. What is its refractive index? (Speed of light in vacuum = 3 × 10⁸ m/s)
Answer: The absolute refractive index (n) of a medium is the ratio of the speed of light in vacuum (c) to the speed of light in that medium (v). n = c/v = (3 × 10⁸)/(2 × 10⁸) = 1.5
26. Distinguish between a real image and a virtual image. Give one example of each.
| Feature | Real Image | Virtual Image |
|---|---|---|
| Formation | Rays actually converge | Rays appear to diverge |
| Nature | Can be projected on screen | Cannot be projected |
| Position | On same side as object (mirror) | Behind mirror / same side as object (lens) |
| Example | Concave mirror beyond F | Plane mirror, convex mirror |
27. What is the new Cartesian sign convention for mirrors? List all the rules.
Answer:
- All distances are measured from the pole (P) of the mirror.
- Distances in the direction of incident light (usually left to right) are positive.
- Distances opposite to incident light are negative.
- Heights above the principal axis are positive.
- Heights below the principal axis are negative.
28. A concave lens has focal length 15 cm. At what distance should an object be placed so that it forms an image at 10 cm from the lens?
u = ?, v = −10 cm (virtual image, same side), f = −15 cm 1/v − 1/u = 1/f 1/(−10) − 1/u = 1/(−15) −1/u = −1/15 + 1/10 = (−2 + 3)/30 = 1/30 u = −30 cm The object should be placed 30 cm in front of the lens.
29. What is meant by the power of a lens? A doctor prescribes a corrective lens of power −2.5 D. What is the focal length and type of lens?
Answer: Power of a lens = 1/focal length (in metres). It measures the degree of convergence or divergence. f = 1/P = 1/(−2.5) = −0.4 m = −40 cm Negative power → Concave (diverging) lens, used to correct myopia.
30. State Snell's Law of refraction.
Answer: Snell's Law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media and a given colour of light. This constant is the refractive index (n) of the second medium with respect to the first: n₁ sin i = n₂ sin r (or sin i / sin r = n₂₁)
SECTION D — Long Answer / Case-Based Questions (5 Marks each)
31. (a) Draw ray diagrams showing image formation by a concave mirror for all six positions of the object. For each, state the nature, position, and size of the image.
(b) A concave mirror has a radius of curvature of 40 cm. An object is placed 60 cm in front of it. Find the image distance, magnification, and nature of the image.
Answer (a):
| Object Position | Image Position | Nature | Size |
|---|---|---|---|
| At infinity | At F | Real, inverted | Highly diminished (point) |
| Beyond C | Between F and C | Real, inverted | Diminished |
| At C | At C | Real, inverted | Same size |
| Between F and C | Beyond C | Real, inverted | Magnified |
| At F | At infinity | Real, inverted | Highly magnified |
| Between P and F | Behind mirror | Virtual, erect | Magnified |
Answer (b): f = −R/2 = −20 cm, u = −60 cm Mirror formula: 1/v + 1/u = 1/f 1/v = 1/f − 1/u = 1/(−20) − 1/(−60) = −3/60 + 1/60 = −2/60 v = −30 cm (real, in front of mirror) m = −v/u = −(−30)/(−60) = −0.5 (real, inverted, diminished)
32. (a) What is refraction of light? State the laws of refraction.
(b) A ray of light passes from air into a glass slab of refractive index 1.5, at an angle of incidence of 30°. Calculate the angle of refraction. (sin 30° = 0.5, sin 19.47° ≈ 0.333)
(c) Why does a pencil appear bent when partially immersed in water?
Answer (a): Refraction is the bending of light when it passes obliquely from one medium to another of different optical density. Laws:
- The incident ray, refracted ray, and normal at the point of incidence are all in the same plane.
- The ratio sin i / sin r = constant (= refractive index), for a given pair of media and wavelength.
Answer (b): n = sin i / sin r → 1.5 = 0.5 / sin r → sin r = 0.5/1.5 = 0.333 r ≈ 19.47°Answer (c): When light from the submerged part of the pencil passes from water (denser) to air (rarer), it bends away from the normal. Our eye traces the refracted ray back in a straight line, making the pencil appear bent or displaced at the water surface.
33. (a) Draw labelled ray diagrams showing image formation by a convex lens for objects placed at: (i) infinity, (ii) between F and 2F, (iii) between F and optical centre.
(b) Two lenses, one convex of focal length 30 cm and one concave of focal length 60 cm, are placed in contact. Find the focal length and power of the combination. State whether the combination is converging or diverging.
Answer (a):
| Position | Image | Nature | Size |
|---|---|---|---|
| At infinity | At F₂ | Real, inverted | Point/highly diminished |
| Between F and 2F | Beyond 2F₂ | Real, inverted | Magnified |
| Between O and F | Same side as object | Virtual, erect | Magnified |
Answer (b): 1/f = 1/f₁ + 1/f₂ = 1/30 + 1/(−60) = 2/60 − 1/60 = 1/60 f = +60 cm = 0.6 m (converging) P = 1/f = 1/0.6 = +1.67 D
34. Case Study: Riya is visiting an eye clinic with her grandfather. The doctor examines him and says he cannot see nearby objects clearly. He prescribes a lens of power +2.5 D.
(a) Name the defect of vision Riya's grandfather is suffering from.
(b) Draw a diagram showing the defect and its correction.
(c) What is the focal length of the prescribed lens?
(d) Name the type of lens used and explain how it corrects the defect.
(e) Riya herself is prescribed −1.5 D lenses. Name her defect and calculate her focal length.
(a) Hypermetropia (far-sightedness) — cannot see nearby objects. (b) (Diagram: eye where image forms behind retina; corrected with convex lens bringing image onto retina.) (c) f = 1/P = 1/2.5 = +0.4 m = +40 cm (d) Convex (converging) lens. It converges the diverging rays from nearby objects so they focus on the retina, not behind it. (e) Riya has myopia (short-sightedness). f = 1/(−1.5) = −0.67 m = −66.7 cm
SECTION E — Very Short / 1-Mark Questions
35. What is the relationship between focal length (f) and radius of curvature (R)?
f = R/2
36. Define magnification for mirrors.
m = −v/u (also = height of image / height of object)
37. A convex mirror always produces what kind of image?
Virtual, erect, diminished
38. What happens when a ray of light is incident normally on a mirror?
It reflects back along the same path (angle of incidence = angle of reflection = 0°)
39. State one use each of concave mirror and convex mirror.
Concave: Shaving/make-up mirror, torches, solar furnaces. Convex: Rear-view mirrors, security mirrors.
40. What is the power of a plane mirror?
Zero (focal length = infinity)
41. What is the optical centre of a lens?
The central point of a lens through which any ray passes without deviation.
42. Can a concave lens form a real image?
No, a concave lens always forms virtual images.
43. What is the unit of refractive index?
It is a dimensionless (unitless) quantity.
44. Why are the bottom of swimming pools appear shallower than they actually are?
Due to refraction — light bends away from normal when going from water (denser) to air (rarer), making the pool appear shallower.
SECTION F — Numericals Practice Set
| Q | Given | Find |
|---|---|---|
| N1 | f = −10 cm (concave), u = −15 cm | v, m |
| N2 | f = +20 cm (convex lens), u = −60 cm | v, m, image nature |
| N3 | Speed of light in medium = 1.5 × 10⁸ m/s | Refractive index |
| N4 | Object height = 4 cm, m = −2 | Image height, image nature |
| N5 | P₁ = +3.5 D, P₂ = −1.5 D (in contact) | Net power, focal length |
Answers:
- N1: 1/v = 1/(−10) − 1/(−15) = −1/30 → v = −30 cm; m = −2 (real, inverted, magnified)
- N2: 1/v = 1/20 + 1/(−60) = 2/60 → v = +30 cm; m = −0.5 (real, inverted, diminished)
- N3: n = (3 × 10⁸)/(1.5 × 10⁸) = 2.0
- N4: Image height = −2 × 4 = −8 cm (real, inverted)
- N5: P = +2.0 D; f = +0.5 m = +50 cm (converging)
Key Formulas to Remember
| Formula | Use |
|---|---|
| 1/v + 1/u = 1/f | Mirror formula |
| 1/v − 1/u = 1/f | Lens formula |
| m = −v/u (mirror) | Magnification (mirror) |
| m = v/u (lens) | Magnification (lens) |
| f = R/2 | Focal length from radius of curvature |
| n = c/v | Refractive index |
| n = sin i / sin r | Snell's law |
| P = 1/f(m) | Power of lens |
| P = P₁ + P₂ | Combined power |
This covers all subtopics: reflection, mirror formula, refraction, Snell's law, lenses, power, refractive index, image formation, sign convention, ray diagrams, defects of vision, and numericals. All question types match CBSE Class 10 board exam pattern.
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