MP Board Class 10 Science Chapter 9: Light – Reflection
MP Board Class 10 Science Chapter 9: Light – Reflection and Refraction (प्रकाश – परावर्तन एवं अपवर्तन) Important Questions — Light is one of the highest-weightage chapters in the MP Board Class 10 Science exam, carrying 12–16 marks across reflection, spherical mirrors, refraction, and lenses. This page compiles the most frequently asked board exam questions — MCQs, short/long answers, numericals, and PYQs from 2017–2026 — to help you score full marks in this chapter.
📑 Table of Contents
- 1. Reflection of Light – Important Questions
- 2. Spherical Mirrors – Important Questions
- 3. Mirror Formula & Sign Convention – Numericals
- 4. Refraction of Light – Important Questions
- 5. Lenses & Lens Formula – Numericals
- 6. Multiple Choice Questions (1 Mark Each)
- 7. Very Short & Short Answer Questions (2–4 Marks)
- 8. Long Answer Questions (5–6 Marks)
- Previous Year Questions (2017–2026)
- Frequently Asked Questions
💡 1. Reflection of Light – Important Questions
Q1. State the two laws of reflection of light.
Answer: The two laws of reflection are:
(i) The angle of incidence (∠i) is always equal to the angle of reflection (∠r).
(ii) The incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence all lie in the same plane.
These laws hold true for both plane mirrors and spherical mirrors.
Q2. What is the difference between a real image and a virtual image?
Answer:
📌 Exam Tip: The question “Differentiate between real and virtual image” appears in almost every MP Board exam — usually 3 marks. Memorise the table above.
Q3. A ray of light is incident on a plane mirror at an angle of 30° with the mirror surface. What will be the angle of reflection?
Answer: Angle with mirror surface = 30°
∴ Angle of incidence (∠i) = 90° − 30° = 60°
By law of reflection, ∠i = ∠r
∴ Angle of reflection (∠r) = 60°
🪞 2. Spherical Mirrors – Important Questions
Q4. Define the following terms related to spherical mirrors: (a) Pole (b) Centre of curvature (c) Focal length (d) Radius of curvature
Answer:
(a) Pole (P): The centre point of the spherical mirror’s reflecting surface.
(b) Centre of curvature (C): The centre of the hollow sphere of which the mirror forms a part.
(c) Focal length (f): The distance between the pole and the principal focus. For spherical mirrors, f = R/2.
(d) Radius of curvature (R): The distance between the pole and the centre of curvature. R = 2f.
Q5. Why is a convex mirror used as a rear-view mirror in vehicles?
Answer: A convex mirror is used as a rear-view mirror because:
(i) It always produces an erect (upright) image.
(ii) It provides a wider field of view — it can show more area behind the vehicle compared to a plane or concave mirror.
(iii) The image formed is diminished, allowing the driver to see multiple vehicles at once.
These properties make convex mirrors ideal for safety while driving.
🔑 Key Fact: Concave mirrors are used in torches, headlights, and shaving mirrors because they converge light to a focal point. Convex mirrors diverge light, giving a wider view.
Q6. An object is placed at a distance of 20 cm from a concave mirror of focal length 15 cm. Find the position and nature of the image.
Answer:
Given: u = −20 cm, f = −15 cm (Concave mirror: f negative as per sign convention)
Using mirror formula: 1/f = 1/v + 1/u
1/v = 1/f − 1/u = 1/(−15) − 1/(−20) = −1/15 + 1/20 = (−4 + 3)/60 = −1/60
v = −60 cm
Magnification m = −v/u = −(−60)/(−20) = 60/(−20) = −3
Since v is negative, the image is formed 60 cm in front of the mirror (on the same side as object). Since m = −3, the image is real, inverted, and magnified 3 times.
📐 3. Mirror Formula & Sign Convention – Numericals
Q7. State the sign convention for spherical mirrors (Cartesian sign convention).
Answer: According to the New Cartesian Sign Convention:
(i) The pole (P) of the mirror is taken as the origin.
(ii) The principal axis is taken as the X-axis.
(iii) Distances measured in the direction of incident light (from the mirror towards the object) are taken as positive.
(iv) Distances measured opposite to the direction of incident light are taken as negative.
(v) Heights measured upwards (perpendicular to principal axis) are taken as positive.
(vi) Heights measured downwards are taken as negative.
Thus for concave mirror: f is −ve, u is −ve. For convex mirror: f is +ve, u is −ve.
Q8. An object 5 cm high is placed at a distance of 30 cm from a convex mirror of focal length 20 cm. Find the position, nature, and size of the image.
Answer:
Given: h = +5 cm, u = −30 cm, f = +20 cm (Convex mirror: f positive)
Using mirror formula: 1/f = 1/v + 1/u
1/v = 1/f − 1/u = 1/20 − 1/(−30) = 1/20 + 1/30 = (3+2)/60 = 5/60 = 1/12
v = +12 cm (Image formed 12 cm behind the mirror — virtual)
Magnification m = −v/u = −12/(−30) = 12/30 = +0.4
h’ = m × h = 0.4 × 5 = +2 cm
The image is virtual, erect, diminished (2 cm tall), located 12 cm behind the mirror.
🧮 Formula Box: Mirror formula: 1/f = 1/v + 1/u | Magnification: m = −v/u = h’/h | f = R/2
🔦 4. Refraction of Light – Important Questions
Q9. 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 constant for a given pair of media. Mathematically:
n₂₁ = sin i / sin r = constant
Where n₂₁ is the refractive index of medium 2 with respect to medium 1. Also, n₁ sin i = n₂ sin r, where n₁ and n₂ are absolute refractive indices of the two media.
Q10. What is the refractive index of a medium? How is it related to the speed of light?
Answer: The 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
The refractive index is always greater than or equal to 1 (since c ≥ v). Higher refractive index means light travels slower in that medium (optically denser). For example, diamond has n = 2.42, so light travels at only 41% of its vacuum speed in diamond.
Q11. What is total internal reflection? Give two natural examples.
Answer: Total internal reflection (TIR) occurs when light travelling from an optically denser medium to a rarer medium strikes the interface at an angle greater than the critical angle. In TIR, 100% of light is reflected back into the denser medium.
Natural examples:
(i) Mirage — In deserts on hot days, light from the sky undergoes TIR in the hot air layer near the ground, creating an illusion of water.
(ii) Sparkling of diamonds — Diamonds have a very high refractive index (2.42) and a low critical angle, causing multiple TIR events inside the diamond.
Q12. Light enters from air to glass having refractive index 1.50. What is the speed of light in glass? (Speed of light in air = 3 × 10⁸ m/s)
Answer:
Given: n = 1.50, c = 3 × 10⁸ m/s
Using n = c/v
v = c/n = (3 × 10⁸) / 1.50 = 2 × 10⁸ m/s
So the speed of light in glass is 2 × 10⁸ m/s.
🔍 5. Lenses & Lens Formula – Numericals
Q13. Differentiate between convex lens and concave lens.
Answer:
Q14. An object 2 cm tall is placed at a distance of 30 cm from a convex lens of focal length 20 cm. Find the position, nature, and size of the image.
Answer:
Given: h = +2 cm, u = −30 cm, f = +20 cm (Convex lens: f positive)
Using lens formula: 1/f = 1/v − 1/u
1/v = 1/f + 1/u = 1/20 + 1/(−30) = 1/20 − 1/30 = (3−2)/60 = 1/60
v = +60 cm (Image formed 60 cm on the opposite side — real)
Magnification m = v/u = 60/(−30) = −2
h’ = m × h = −2 × 2 = −4 cm
The image is real, inverted, magnified (4 cm tall), located 60 cm on the opposite side of the lens.
Q15. A concave lens of focal length 15 cm forms an image 10 cm from the lens. Find the object distance.
Answer:
Given: f = −15 cm (Concave lens: f negative), v = −10 cm (Image formed on same side — virtual)
Using lens formula: 1/f = 1/v − 1/u
1/u = 1/v − 1/f = 1/(−10) − 1/(−15) = −1/10 + 1/15 = (−3 + 2)/30 = −1/30
u = −30 cm
So the object is placed 30 cm in front of the concave lens.
📝 6. Multiple Choice Questions (1 Mark Each)
MCQs from Light chapter appear frequently in the MP Board exam. Here are 10 must-practice questions:
- The image formed by a plane mirror is always:
(a) Real and inverted (b) Virtual and erect ✓ (c) Real and erect (d) Virtual and inverted - The focal length of a concave mirror with radius of curvature 40 cm is:
(a) 40 cm (b) 80 cm (c) 10 cm (d) 20 cm ✓ - Which mirror is used as a rear-view mirror in vehicles?
(a) Plane mirror (b) Concave mirror (c) Convex mirror ✓ (d) Cylindrical mirror - Speed of light in vacuum is:
(a) 2 × 10⁸ m/s (b) 3 × 10⁸ m/s ✓ (c) 3 × 10⁶ m/s (d) 2 × 10⁶ m/s - The refractive index of a medium is always:
(a) Less than 1 (b) Exactly 1 (c) Greater than or equal to 1 ✓ (d) Zero - When light travels from a rarer to a denser medium, it:
(a) Bends away from normal (b) Bends towards the normal ✓ (c) Does not bend (d) Reflects completely - The power of a lens of focal length 25 cm is:
(a) 4 D ✓ (b) 2.5 D (c) 0.25 D (d) −4 D
(P = 1/f in metres = 1/0.25 = 4 D) - A convex lens of focal length 10 cm is used as a magnifying glass. For maximum magnification, the object should be placed:
(a) At infinity (b) At 2F (c) At F (d) Between F and the optical centre ✓ - Which of the following has the highest refractive index?
(a) Water (b) Crown glass (c) Diamond ✓ (d) Kerosene - The SI unit of power of a lens is:
(a) Metre (b) Watt (c) Dioptre ✓ (d) Joule
✏️ 7. Very Short & Short Answer Questions (2–4 Marks)
-
What is the principal focus of a concave mirror?
The principal focus of a concave mirror is the point on its principal axis where light rays parallel to the principal axis converge after reflection. It is represented by F and lies in front of the mirror. (2 marks) -
Define 1 dioptre of power of a lens.
One dioptre is the power of a lens whose focal length is 1 metre. Power P = 1/f (in metres). A convex lens has positive power and a concave lens has negative power. (2 marks) -
Why does a ray of light bend when it enters a different medium?
Light bends at the interface between two media because its speed changes. When light enters a denser medium, it slows down and bends towards the normal. When it enters a rarer medium, it speeds up and bends away from the normal. This bending is called refraction. (2 marks) -
What is the relationship between focal length and radius of curvature for a spherical mirror?
For a spherical mirror, the focal length (f) is half the radius of curvature (R). Mathematically: f = R/2. For a concave mirror, both f and R are taken as negative, and for a convex mirror, both are positive as per sign convention. (2 marks) -
Draw a ray diagram showing the image formed by a convex mirror when the object is placed anywhere in front of it.
A convex mirror always forms a virtual, erect, and diminished image behind the mirror, regardless of the object’s position. A ray parallel to the principal axis appears to diverge from the focus after reflection, and a ray directed towards the centre of curvature reflects back along the same path. The intersection of these reflected rays extended backward gives the virtual image. (3 marks) -
Explain why the bottom of a pond appears raised when viewed from above.
This is due to refraction of light. Light rays from the bottom of the pond travel from water (denser medium) to air (rarer medium). They bend away from the normal at the water-air interface. To the observer, the bent rays appear to come from a point higher than the actual bottom, making the pond look shallower than it really is. This apparent depth = real depth / refractive index of water. (3 marks) -
A concave mirror produces a real, inverted image of the same size as the object. Where is the object placed?
The object must be placed at the centre of curvature (C) of the concave mirror. At this position, the image is formed at C itself — it is real, inverted, and of the same size as the object. The magnification is −1. If asked for focal length, C = 2f. (3 marks) -
Light enters from air to diamond. If the refractive index of diamond is 2.42, calculate the speed of light in diamond. (c = 3 × 10⁸ m/s)
n = c/v ⇒ v = c/n = 3 × 10⁸ / 2.42 = 1.24 × 10⁸ m/s. So light travels at about 1.24 × 10⁸ m/s in diamond, which is only about 41% of its speed in vacuum. (4 marks) -
An object 4 cm high is placed 15 cm from a convex mirror of focal length 10 cm. Find the image distance and height.
Given: h = +4 cm, u = −15 cm, f = +10 cm. 1/v = 1/f − 1/u = 1/10 + 1/15 = 5/30 = 1/6. v = +6 cm. m = −v/u = −6/(−15) = 0.4. h’ = 0.4 × 4 = 1.6 cm. Image is virtual, erect, 1.6 cm tall, 6 cm behind the mirror. (4 marks) -
Define power of a lens. A convex lens has a focal length of 40 cm in air. Find its power.
Power of a lens (P) is the reciprocal of its focal length in metres. P = 1/f (in metres). For f = 40 cm = 0.4 m, P = 1/0.4 = +2.5 D. Positive power indicates it is a converging lens. (3 marks)
📖 8. Long Answer Questions (5–6 Marks)
Q16. (a) State the laws of reflection. (b) With the help of a ray diagram, explain the image formation by a concave mirror when the object is placed between its pole and focus. Mention the nature, position, and size of the image. (c) List three uses of concave mirrors.
Answer:
(a) Laws of Reflection:
(i) Angle of incidence equals angle of reflection (∠i = ∠r).
(ii) Incident ray, reflected ray, and normal at the point of incidence all lie in the same plane.
(b) Object between Pole (P) and Focus (F) of Concave Mirror:
When an object is placed between P and F of a concave mirror:
— A ray parallel to the principal axis passes through F after reflection.
— A ray directed towards the centre of curvature (C) reflects back along the same path.
— These reflected rays diverge; their extensions behind the mirror intersect to form the image.
Image characteristics: Virtual, erect, magnified, and formed behind the mirror.
This is why concave mirrors are used as shaving mirrors and by dentists — they produce an enlarged, upright image.
(c) Uses of Concave Mirrors:
(i) Shaving mirrors — produce enlarged, erect image of face.
(ii) Headlights and torches — light source placed at focus produces parallel beam.
(iii) Solar furnaces — concentrate sunlight to a point for heating. (5 marks)
Q17. (a) State the lens formula and magnification formula for lenses. (b) A convex lens of focal length 15 cm produces an image 30 cm from the lens on the opposite side. Calculate the object distance. (c) What is the power of this lens?
Answer:
(a) Lens Formulas:
Lens formula: 1/f = 1/v − 1/u
Magnification: m = v/u = h’/h
Power of lens: P = 1/f (in metres), unit = dioptre (D)
(b) Given: f = +15 cm (convex), v = +30 cm (opposite side — real image)
Using: 1/f = 1/v − 1/u
1/u = 1/v − 1/f = 1/30 − 1/15 = (1 − 2)/30 = −1/30
u = −30 cm
The object is placed 30 cm in front of the convex lens.
(c) Power of lens: f = 15 cm = 0.15 m
P = 1/0.15 = +6.67 D
The positive power confirms it is a converging (convex) lens. (6 marks)
Q18. (a) Explain the phenomenon of refraction through a glass slab with a labelled diagram. (b) A ray of light enters from air into a glass slab at an angle of 45°. If the refractive index of glass is 1.5, find the angle of refraction. (Given sin 45° = 0.707)
Answer:
(a) Refraction through a Glass Slab:
When a ray of light passes through a rectangular glass slab:
(i) It bends towards the normal at the first surface (air → glass).
(ii) It travels in a straight line inside the glass.
(iii) It bends away from the normal at the second surface (glass → air).
(iv) The emergent ray is parallel to the incident ray but laterally displaced.
(v) The lateral displacement depends on the thickness of the slab, refractive index, and angle of incidence.
Key observation: Light passing through a parallel-sided glass slab emerges parallel to the incident ray — no net deviation, only sideways shift.
(b) Given: i = 45°, n = 1.5, sin 45° = 0.707
Using Snell’s law: n = sin i / sin r
sin r = sin i / n = 0.707 / 1.5 = 0.471
r = sin⁻¹(0.471) ≈ 28°
So the angle of refraction in glass is approximately 28°. (6 marks)
📋 Previous Year Questions (2017–2026)
The Light chapter has consistently contributed 12–16 marks in MP Board exams. Here are the actual questions asked in recent years:
❓ Frequently Asked Questions
Q1. How many marks does the Light chapter carry in MP Board Class 10 Science?
The Light chapter (Chapter 9 + Chapter 10 — The Human Eye) collectively carries 12–16 marks in the MP Board Class 10 Science exam. This makes it one of the highest-weightage chapters in the syllabus.
Q2. What is the difference between concave and convex mirrors?
A concave mirror has a reflecting surface that curves inward (like a cave) and converges light to a focus. A convex mirror has a reflecting surface that bulges outward and diverges light. Concave mirrors can form both real and virtual images; convex mirrors always form virtual, erect, and diminished images.
Q3. What is the mirror formula and when is it used?
The mirror formula is 1/f = 1/v + 1/u, where f is focal length, v is image distance, and u is object distance. It is used to calculate the position of the image formed by spherical mirrors when the object position and focal length are known.
Q4. What is Snell’s law in simple words?
Snell’s law says that when light passes from one medium to another, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for that pair of media. This constant is called the refractive index.
Q5. What is the power of a lens and its unit?
Power of a lens is the measure of its ability to converge or diverge light rays. It is defined as the reciprocal of focal length in metres (P = 1/f). The SI unit is dioptre (D). A convex lens has positive power and a concave lens has negative power.
Q6. Why does a pencil appear bent in water?
This happens due to refraction of light. Light from the submerged part of the pencil travels from water (denser) to air (rarer), bending away from the normal. The brain traces the rays back in straight lines, making the pencil appear bent or broken at the water surface.
Q7. What is the sign convention for lenses in numerical problems?
According to the Cartesian sign convention: distances measured in the direction of incident light are positive, opposite direction is negative. For a convex lens, f is positive; for a concave lens, f is negative. Object distance (u) is always negative. Heights above principal axis are positive, below are negative.
Q8. How to solve mirror and lens numericals step by step?
Step 1: Write given values with proper sign convention. Step 2: Identify the correct formula (mirror: 1/f = 1/v + 1/u, lens: 1/f = 1/v − 1/u). Step 3: Substitute and solve for unknown. Step 4: Use magnification formula m = −v/u (mirror) or m = v/u (lens). Step 5: State the nature (real/virtual, erect/inverted, magnified/diminished) and position of the image.
Q9. What is total internal reflection and its conditions?
Total internal reflection is the complete reflection of light within a denser medium. Conditions: (i) Light must travel from denser to rarer medium. (ii) Angle of incidence must be greater than the critical angle for that pair of media. Applications include optical fibres, endoscopes, and diamond sparkle.
Q10. Which topics from Light are most important for MP Board 2027?
Focus on: Laws of reflection and refraction, mirror formula numericals, lens formula numericals, sign convention, ray diagrams for concave/convex mirrors and lenses, power of lens, refractive index based problems, total internal reflection, and the human eye defects (myopia, hypermetropia).
Q11. What is the refractive index of water, glass, and diamond?
Water = 1.33, Crown glass = 1.52, Diamond = 2.42. Higher refractive index means slower light speed in that medium. Diamond’s high refractive index (2.42) gives it a low critical angle of about 24°, causing the beautiful sparkle through multiple total internal reflections.
Q12. Can I score full marks in the Light chapter with these questions?
Yes, these important questions cover the entire MP Board syllabus for Light — Reflection and Refraction. Practice all the MCQs, numericals, and long answer questions above. Make sure you can draw ray diagrams clearly and apply the correct sign convention for mirror and lens formula problems. Solving the PYQ table questions will give you a strong idea of the exam pattern.