Important Questions Class 10 Science Chapter 9: Light Reflection and Refraction

Light: Reflection and Refraction is Chapter 9 of Class 10 NCERT Science (Reprint 2026-27). The chapter studies how light behaves when it hits a polished surface or passes from one medium to another. It covers spherical mirrors, refraction through glass slabs, refractive index, spherical lenses, and the power of a lens.

Important questions class 10 science chapter 9 on this page cover MCQs, very short answers, short answers, long answers, numericals, ray diagrams, extra questions, and previous year question patterns. All content follows the NCERT chapter structure and the CBSE 2026 syllabus.

This chapter tests two very distinct skills: writing correct ray diagrams and solving numerical problems using sign conventions. A student who confuses the mirror formula with the lens formula, or applies the wrong sign to the focal length, loses marks on every numerical in this section. A student who draws labelled ray diagrams and applies the New Cartesian Sign Convention correctly scores full marks consistently. Use Important Questions Class 10 Science Chapter 8 for the previous chapter and Important Questions Class 10 Science Chapter 10 for the next.

Key Takeaways

Introduction to Class 10 Science Chapter 9 Light Reflection and Refraction

The NCERT chapter builds through two main parts. Sections 9.1 and 9.2 cover reflection: laws of reflection, types of spherical mirrors, image formation by concave and convex mirrors, sign convention, mirror formula, and magnification. Section 9.3 covers refraction: laws of refraction, glass slab refraction, refractive index, spherical lenses, lens formula, magnification, and power of a lens.

Three areas carry the most marks in CBSE 2026 board exams. First, image formation by mirrors and lenses: students must know the complete table of image positions for each object position. Second, mirror formula and lens formula numericals: these appear in almost every board paper. Third, ray diagram questions: CBSE frequently asks students to draw labelled ray diagrams for specific image characteristics.

The key rule that connects both halves of the chapter is the New Cartesian Sign Convention. All distances are measured from the pole (for mirrors) or optical centre (for lenses). Applying signs incorrectly is the most common reason students lose marks in numericals.

Important Topics in Light Reflection and Refraction Class 10

Every board question from this chapter maps to one of these concept areas. These cbse class 10 light reflection and refraction important questions cover all seven major topic clusters.

• Reflection of light: A highly polished surface reflects most of the light falling on it. The angle of incidence equals the angle of reflection. The incident ray, normal, and reflected ray all lie in the same plane.
• Spherical mirrors: A concave mirror curves inwards. A convex mirror bulges outwards. Key terms include pole (P), centre of curvature (C), principal axis, principal focus (F), focal length (f), and aperture. The relationship R = 2f holds for spherical mirrors of small aperture.
• Sign convention for mirrors: All distances are measured from the pole P. Distances in the direction of incident light (to the right) are positive. Distances opposite to incident light (to the left) are negative.
• Mirror formula and magnification: Mirror formula: 1/v + 1/u = 1/f. Magnification: m = h'/h = -v/u. A negative magnification means the image is real and inverted. A positive magnification means the image is virtual and erect.
• Laws of refraction (Snell's law): The incident ray, refracted ray, and normal all lie in the same plane. The ratio of sin i to sin r is a constant for a given pair of media.
• Refractive index: n = speed of light in vacuum / speed of light in medium = c/v. A medium with a higher refractive index is optically denser.
• Lens formula and power: Lens formula: 1/v - 1/u = 1/f. Power: P = 1/f (f in metres). Unit is dioptre (D). Power of convex lens is positive. Power of concave lens is negative.

Light Reflection and Refraction Class 10 MCQs with Answers

These class 10 light reflection and refraction important questions in MCQ format cover all major concept clusters. Attempt each before checking the answer.

Q1. Which one of the following materials cannot be used to make a lens? (a) Water (b) Glass (c) Plastic (d) Clay (d) Clay. A lens requires a transparent material. Clay is opaque and cannot transmit light.

Q2. The image formed by a concave mirror is virtual, erect and larger than the object. The object is placed: (a) Between C and F (b) At C (c) Beyond C (d) Between the pole and F (d) Between the pole P and the principal focus F. This is the only position where a concave mirror gives a virtual, erect, enlarged image.

Q3. No matter how far you stand from a mirror, your image appears erect. The mirror is most likely: (a) Only concave (b) Only convex (c) Either plane or convex (d) Only plane (c) Either plane or convex. Both always give virtual, erect images regardless of object distance.

Q4. Where should an object be placed in front of a convex lens to get a real image of the same size as the object? (a) At the principal focus (b) At twice the focal length (c) At infinity (d) Between O and F (b) At twice the focal length (at 2F1). The image forms at 2F2, the same size, real and inverted.

Q5. A spherical mirror and a thin spherical lens both have focal lengths of -15 cm. They are likely to be: (a) Both concave (b) Both convex (c) Mirror concave, lens convex (d) Mirror convex, lens concave (d) Mirror is convex, lens is concave. A negative focal length indicates a convex mirror and a concave lens under the sign convention.

Q6. Which of the following lenses should you use while reading small letters in a dictionary? (a) Convex lens of focal length 50 cm (b) Concave lens of focal length 50 cm (c) Convex lens of focal length 5 cm (d) Concave lens of focal length 5 cm (c) Convex lens of focal length 5 cm. A convex lens of shorter focal length gives a more magnified virtual image.

Q7. A ray of light travelling in air enters obliquely into water. The ray bends: (a) Away from the normal (b) Towards the normal (c) Remains undeviated (d) Along the normal (b) Towards the normal. Water is optically denser than air. Light slows down and bends towards the normal when entering a denser medium.

Q8. The power of a concave lens of focal length 2 m is: (a) +2 D (b) -2 D (c) +0.5 D (d) -0.5 D (d) -0.5 D. P = 1/f = 1/(-2) = -0.5 D. Concave lenses have negative power.

Very Short Answer Questions from Light Reflection and Refraction

One-mark and two-mark questions test direct recall and definitions. These light reflection and refraction class 10 questions and answers cover the most tested factual items.

Q9. Define the principal focus of a concave mirror. The principal focus of a concave mirror is the point on the principal axis where all rays parallel to the principal axis converge after reflection. It lies in front of the mirror.

Q10. The radius of curvature of a spherical mirror is 20 cm. What is its focal length? Focal length f = R/2 = 20/2 = 10 cm.

Q11. Name a mirror that can give an erect and enlarged image of an object. A concave mirror gives an erect and enlarged image when the object is placed between the pole (P) and the principal focus (F).

Q12. Why do we prefer a convex mirror as a rear-view mirror in vehicles? A convex mirror always gives a virtual, erect, and diminished image regardless of object distance. It has a wider field of view than a plane mirror, allowing the driver to see a larger area of traffic behind the vehicle.

Q13. Define 1 dioptre of power of a lens. 1 dioptre is the power of a lens whose focal length is exactly 1 metre. 1 D = 1 m-1.

Q14. What is the refractive index of diamond, and what does it mean? The refractive index of diamond is 2.42. This means the speed of light in vacuum is 2.42 times the speed of light inside diamond. Diamond is optically very dense.

Q15. What happens to the emergent ray in refraction through a rectangular glass slab? The emergent ray exits the glass slab parallel to the incident ray, but it is laterally displaced. The bending at the two parallel faces is equal and opposite, so the direction is preserved but the ray shifts sidewards.

Short Answer Questions on Spherical Mirrors

Board exams frequently ask 2-mark and 3-mark questions on mirror properties, sign convention, and mirror formula. These class 10 light reflection and refraction question answer items cover the most tested short-answer formats in CBSE 2026 papers.

Q16. Name the type of mirror used in: (a) headlights of a car, (b) side/rear-view mirror of a vehicle, (c) solar furnace. Give reasons. (a) Concave mirror: it produces powerful parallel beams of light when a source is placed at its focus. (b) Convex mirror: it provides an erect, diminished image with a wider field of view. (c) Large concave mirror: it concentrates sunlight at its focus to produce very high temperatures.

Q17. We wish to obtain an erect image of an object using a concave mirror of focal length 15 cm. What should be the range of object distance? The object must be placed between the pole (P) and the principal focus (F), that is, at a distance less than 15 cm from the mirror. The image formed is virtual, erect, and magnified.

Q18. The magnification produced by a plane mirror is +1. What does this mean? A magnification of +1 means the image is the same size as the object. The positive sign means the image is virtual and erect. The image in a plane mirror is always virtual, erect, and the same size as the object.

Q19. An object 5.0 cm in length is placed at 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature, and size of the image. f = R/2 = +15 cm (convex mirror), u = -20 cm. 1/v = 1/f - 1/u = 1/15 - 1/(-20) = 1/15 + 1/20 = (4 + 3)/60 = 7/60. v = +60/7 = +8.57 cm (behind the mirror). m = -v/u = -(60/7)/(-20) = +3/7 ≈ +0.43. Image height = 0.43 x 5 = 2.14 cm. The image is virtual, erect, and diminished, formed 8.57 cm behind the mirror.

Q20. A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located? m = -3 (real and inverted), u = -10 cm. m = -v/u → -3 = -v/(-10) → v = -30 cm. The image is located 30 cm in front of the concave mirror. It is real and inverted.

Short Answer Questions on Refraction and Refractive Index

These light reflection and refraction class 10 extra questions on refraction cover the laws of refraction, refractive index calculations, and glass slab refraction.

Q21. State the two laws of refraction of light. First law: The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane. Second law (Snell's law): 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: sin i / sin r = constant.

Q22. Light enters from air to glass having refractive index 1.50. What is the speed of light in glass? Speed of light in vacuum is 3 x 10^8 m/s. n = c/v → v = c/n = (3 x 10^8)/1.50 = 2 x 10^8 m/s.

Q23. You are given kerosene, turpentine, and water. In which does light travel fastest? Light travels fastest in the medium with the lowest refractive index. Water = 1.33, kerosene = 1.44, turpentine = 1.47. So light travels fastest in water.

Q24. Find the medium with the highest optical density from the NCERT table. Also name the medium with the lowest optical density. Diamond (refractive index 2.42) has the highest optical density. Air (refractive index 1.0003) has the lowest optical density.

Q25. In a rectangular glass slab, does the emergent ray deviate from the original incident ray direction? Explain. No, the emergent ray is parallel to the incident ray. Refraction occurs at both air-glass and glass-air interfaces. The bending at the two parallel faces is equal and opposite, so the ray exits in the same direction as it entered. However, there is a lateral (sideward) shift in the ray's position.

Long Answer Questions on Lenses and Ray Diagrams

These light reflection and refraction class 10 questions and answers on lenses require structured, step-by-step working. Write the formula, substitute values, and state the nature of the image for full marks in CBSE 2026 board papers.

Q26. An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of focal length 15.0 cm. Find the image distance. Also find the nature and size of the image. h = +4.0 cm, u = -25.0 cm, f = -15.0 cm. 1/v = 1/f - 1/u = 1/(-15) - 1/(-25) = -1/15 + 1/25 = (-5 + 3)/75 = -2/75. v = -37.5 cm. m = -v/u = -(-37.5)/(-25) = -1.5. h' = m x h = -1.5 x 4 = -6.0 cm. The image is real, inverted, and enlarged (6 cm tall), formed 37.5 cm in front of the mirror.

Q27. A concave lens has focal length 15 cm. At what distance should an object be placed to form an image at 10 cm from the lens? Find the magnification. v = -10 cm, f = -15 cm. 1/u = 1/v - 1/f = 1/(-10) - 1/(-15) = -1/10 + 1/15 = (-3 + 2)/30 = -1/30. u = -30 cm (object placed 30 cm in front of the lens). m = v/u = (-10)/(-30) = +1/3 ≈ +0.33. The image is virtual, erect, and one-third the size of the object.

Q28. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The object is 15 cm from the lens. Find the nature, position, and size of the image. h = +2.0 cm, f = +10 cm, u = -15 cm. 1/v = 1/f + 1/u = 1/10 + 1/(-15) = 1/10 - 1/15 = (3 - 2)/30 = 1/30. v = +30 cm (real image on opposite side of lens). m = v/u = 30/(-15) = -2. h' = -2 x 2 = -4.0 cm. The image is real, inverted, enlarged (4 cm tall), formed 30 cm on the other side of the lens.

Q29. A convex lens forms a real and inverted image of a needle at 50 cm from it. The image is the same size as the needle. Where is the needle placed? Find the power of the lens. Image same size as object → m = -1 → object is at 2F. Since image is at 50 cm, object is also at 50 cm in front: u = -50 cm, v = +50 cm. 1/f = 1/v - 1/u = 1/50 - 1/(-50) = 1/50 + 1/50 = 2/50. f = +25 cm = 0.25 m. P = 1/f = 1/0.25 = +4 D.

Q30. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. Find screen distance and image size. h = +7.0 cm, u = -27 cm, f = -18 cm. 1/v = 1/f - 1/u = 1/(-18) - 1/(-27) = -1/18 + 1/27 = (-3 + 2)/54 = -1/54. v = -54 cm (screen 54 cm in front of mirror). m = -v/u = -(-54)/(-27) = -2. h' = -2 x 7 = -14 cm. The image is real, inverted, and enlarged (14 cm tall), formed 54 cm in front of the mirror.

Light Reflection and Refraction Numericals for Class 10

These light reflection and refraction class 10 important questions with answers in numerical format follow the NCERT exercise pattern. These are high-probability board questions for CBSE 2026 exams.

Q31. Find the focal length of a convex mirror whose radius of curvature is 32 cm. f = R/2 = 32/2 = +16 cm. The positive sign indicates a convex mirror.

Q32. An object is placed at 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. u = -10 cm, f = +15 cm. 1/v = 1/f - 1/u = 1/15 - 1/(-10) = 1/15 + 1/10 = (2 + 3)/30 = 5/30. v = +6 cm (behind the mirror). Image is virtual, erect, and diminished.

Q33. A doctor prescribes a corrective lens of power +1.5 D. Find the focal length. Is the lens converging or diverging? f = 1/P = 1/1.5 = +0.67 m = +66.7 cm. Positive focal length means it is a convex (converging) lens.

Q34. Find the power of a concave lens of focal length 2 m. P = 1/f = 1/(-2) = -0.5 D.

Q35. A convex mirror used as a rear-view mirror has a radius of curvature of 3.00 m. A bus is 5.00 m from this mirror. Find the position, nature, and size of the image. R = +3.00 m, f = R/2 = +1.50 m, u = -5.00 m. 1/v = 1/f - 1/u = 1/1.50 + 1/5.00 = (5 + 1.5)/7.5 = 6.5/7.5. v ≈ +1.15 m (behind mirror). m = -v/u = -(1.15)/(-5.00) = +0.23. Image is virtual, erect, and diminished (0.23 times the size of the bus).

Q36. Find the focal length of a lens of power -2.0 D. What type of lens is this? f = 1/P = 1/(-2.0) = -0.5 m = -50 cm. Negative focal length means it is a concave (diverging) lens.

Ray Diagram Questions from Light Reflection and Refraction

Ray diagrams carry 2 to 3 marks in board exams. These light reflection and refraction important questions on ray diagrams require correct labels, arrows on rays, and image identification. Students lose marks by drawing unlabelled diagrams or using wrong ray paths.

Q37. Draw a ray diagram to show how a concave mirror forms a real, inverted, enlarged image of an object placed between C and F. Place object AB between C and F. Draw two rays from tip A: one parallel to principal axis (reflects through F), one through C (reflects back along same path). The two reflected rays meet beyond C on the same side as the object. The image A'B' is real, inverted, and enlarged. Label P, F, C, object, and image.

Q38. When an object is placed between P and F of a concave mirror, what is the nature of the image? Describe the ray diagram. Draw the object between P and F. A ray parallel to the principal axis reflects through F. A ray directed towards C reflects back along the same path. The two reflected rays diverge. Their extensions behind the mirror meet at the image. The image is virtual, erect, and enlarged. It forms behind the mirror.

Q39. Draw a ray diagram to show the image formed by a convex lens when the object is beyond 2F1. Object AB is placed beyond 2F1. Draw ray 1 parallel to principal axis: it refracts through F2. Draw ray 2 through optical centre O: it passes undeviated. Rays meet between F2 and 2F2 on the other side. Image A'B' is real, inverted, and diminished. Label 2F1, F1, O, F2, 2F2, object, and image.

Q40. One-half of a convex lens is covered with black paper. Will it produce a complete image? Explain. Yes, a complete image still forms. The uncovered half of the lens refracts sufficient rays from the object to form a complete image on the screen. However, the image is less bright because fewer rays pass through the lens.

Light Reflection and Refraction Extra Questions Class 10

These light reflection and refraction class 10 extra questions go beyond standard NCERT exercises. They appear in pre-board and CBSE 2026 school assessments.

Q41. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed? v = -10 cm (image on same side as object for concave lens), f = -15 cm. 1/u = 1/v - 1/f = 1/(-10) - 1/(-15) = -1/10 + 1/15 = (-3 + 2)/30 = -1/30. u = -30 cm. The object is placed 30 cm in front of the lens.

Q42. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Find the position, size, and nature of the image. h = 5 cm, u = -25 cm, f = +10 cm. 1/v = 1/f + 1/u = 1/10 + 1/(-25) = 1/10 - 1/25 = (5 - 2)/50 = 3/50. v = +50/3 ≈ +16.67 cm. m = v/u = (50/3)/(-25) = -2/3. h' = (-2/3) x 5 = -3.33 cm. Image is real, inverted, diminished (3.33 cm tall), formed 16.67 cm on the other side of the lens.

Q43. Why does a pencil partly immersed in water appear bent at the water surface? Light from the submerged part travels from water (denser medium) to air (rarer medium) and bends away from the normal. The observer's eye traces these refracted rays straight back, creating a virtual image that appears displaced. This makes the pencil look bent at the water surface.

Q44. The refractive index of glass is 1.5. Find the speed of light in glass if the speed of light in vacuum is 3 x 10^8 m/s. v = c/n = (3 x 10^8)/1.5 = 2 x 10^8 m/s.

Class 10 Chapter 9 Question Answers on Reflection and Refraction

These class 10 science light reflection and refraction question answer items cover conceptual reasoning questions that appear as 2-mark and 3-mark items in CBSE 2026 board papers.

Q45. What is the relationship between radius of curvature and focal length of a spherical mirror? For spherical mirrors of small aperture, the radius of curvature R is equal to twice the focal length f: R = 2f, or f = R/2. The principal focus lies exactly midway between the pole and the centre of curvature.

Q46. What is the difference between real and virtual images formed by a concave mirror? Real images form when reflected rays actually meet at a point in front of the mirror. They can be caught on a screen. Virtual images form when reflected rays appear to diverge from a point behind the mirror. They cannot be caught on a screen. A concave mirror forms real images for objects beyond F and a virtual image only when the object is between P and F.

Q47. Explain why the refractive index of kerosene is greater than that of water even though kerosene is less dense in mass than water. Optical density and mass density are different properties. Refractive index depends on the speed of light in the medium, not on mass density. Kerosene has a refractive index of 1.44 and water has 1.33, so light travels more slowly in kerosene. Kerosene is optically denser than water despite having lower mass density.

Q48. Compare the image formation properties of a concave lens and a convex lens. A concave lens always gives a virtual, erect, and diminished image for any object position. A convex lens gives different images depending on object position: a virtual, erect, enlarged image when the object is between F and O; a real, inverted image of varying sizes for all other positions.