Chapter 9: Light – Reflection and Refraction

Important questions — the ones the board asked most (20)

1. Q1Long answer5 marksAsked: 2024

   (a) Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer. (b) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine the distance of the image from the optical centre of the lens.

2. Q2Long answer5 marksAsked: 2024

   (a) The variation of image distance (v) with object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions that follow : (i) Without calculation, find the focal length of the convex lens. Justify your answer. (ii) Which observation is not correct ? Why ? Draw ray diagram to find the position of the image formed for this position of the object. (iii) Find the approximate value of magnification for u = - 30 cm. OR (b) (i) Define principal axis of a lens. Draw a ray diagram to show what happens when a ray of light parallel to the principal axis of a concave lens passes through it. (ii) The focal length of a concave lens is 20 cm. At what distance from the lens should a 5 cm tall object be placed so that its image is formed at a distance of 15 cm from the lens ? Also calculate the size of the image formed.

3. Q3Long answer5 marksAsked: 2025

   36. (a) (i) "In the refraction of light passing through a rectangular glass slab, the emergent ray is always parallel to the direction of the incident ray." Why? Explain with the help of a ray diagram. What happens when a light ray is incident normally on one of the faces of a rectangular glass prism? Draw the diagram. (ii) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 20 cm. Use the lens formula to determine the position of the image formed. OR (b) (i) A student wants to study the formation of image by a concave mirror using a candle flame as an object. Write the type of image formed by the mirror and also mention the changes in the image formed that the student will observe as the candle flame is moved slowly away from the pole of the mirror. Draw the ray diagram to show the formation of image by the mirror in that situation when the object distance is approximately equal to the radius of curvature of the mirror. (ii) The focal length of a convex mirror used as a rear-view mirror in an automobile is 3.0 m. If a bus is located at a distance of 6.0 m from this mirror, find the position of the image of the bus seen in the mirror using the mirror formula.

   

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   Model answer · Image formation, concave mirror

   1. 1.(b) (i) A concave mirror forms two types of image of the candle flame. When the candle is beyond the principal focus F, the image is real and inverted. When the candle is between the pole P and the principal focus F, the image is virtual and erect.1 mark
   2. 2.As the candle flame is moved slowly away from the pole of the mirror, the image gets diminished, which means it becomes smaller and smaller.1 mark
   3. 3.Ray diagram for the object at the centre of curvature C: a ray from the top of the flame that runs parallel to the principal axis passes through F after reflection. A second ray from the top that passes through F comes out parallel to the principal axis after reflection. The two reflected rays meet at C, below the principal axis. The image is formed at C. It is real, inverted and the same size as the object.1 mark
   4. 4.(ii) Given: object distance, u = – 6.00 m; image distance, v = ?; focal length of the convex mirror, f = + 3.00 m. Mirror formula: 1/v + 1/u = 1/f, or 1/v = 1/f – 1/u0.5 marks
   5. 5.1/v = 1/(+3.00 m) – 1/(– 6.00 m)0.5 marks
   6. 6.= 1/(+3.00 m) + 1/(6.00 m) = (2 + 1)/6 m0.5 marks
   7. 7.or v = 6/3 = + 2.0 m The image of the bus forms 2.0 m behind the mirror. It is virtual, erect and diminished.0.5 marks

   Diagram: Draw a concave mirror with its principal axis, and mark the pole P, the principal focus F and the centre of curvature C. Draw the candle flame (object AB) standing at C. Draw two rays from its top: one parallel to the principal axis that reflects through F, and one through F that reflects parallel to the axis. Mark the inverted, same-size real image A'B' at C, below the axis, with arrowheads on all rays.

   • Write both cases with their positions: "real and inverted" when the candle is beyond F, and "virtual and erect" when it is between P and F.
   • In the numerical, take u = – 6.00 m and f = + 3.00 m, then give the answer with its unit and sign: v = + 2.0 m, behind the mirror.
   • On the diagram, label P, F and C, put arrowheads on the rays, and draw the image at C, inverted and the same size as the object.

   Marks split as in the board’s published marking scheme

4. Q4Long answer5 marksAsked: 2025

   (a) (i) "In refraction of light through a rectangular glass slab, the emergent ray is always parallel to the direction of the incident ray." Why ? Explain with the help of a ray diagram. What happens when a ray of light falls normally on one of the faces of a rectangular glass prism ? Draw diagram. (ii) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 20 cm. Use Lens formula to determine the position of the image formed in this case. OR (b) (i) A student wishes to study the image formation by a concave mirror using candle flame as object. State the type of the image formed by the mirror and mention the change in the image formed, if any, that he observes when the candle flame is gradually moved away from the pole of the mirror. Draw a ray diagram to show the image formation when the object distance is nearly equal to the radius of curvature of the mirror. (ii) A convex mirror used for rear-view on an automobile has a focal length of 3.0 m. If a bus is located at 6.0 m from this mirror, use mirror formula to find the position of the image of the bus as seen in the mirror.

   How the model answer begins

   1. (b) (i) The concave mirror forms a real and inverted image when the candle flame is beyond the principal focus (F). It forms a virtual and erect image, larger than the flame, when the flame is between the pole (P) and…

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5. Q5Long answer5 marksAsked: 2025

   36. (A) (a) Observe the following diagram and compare the three media A, B and C for (i) speed of light and (ii) optical densities. Also justify your answer for any one of the two cases in terms of refractive indices of A, B and C. (b) If a ray of light travelling in medium A falls on medium B, redraw the path of the ray of light in all the three media, if (i) it falls obliquely and the optical density of medium B is made more than that of A and C. (ii) the ray falls normally from medium A on medium B. or (B) Analyse the following observation table showing the variation of image distance (v) with object distance (u) in case of a convex lens and answer the following questions without doing any calculation: | Observation No. | Object distance (u) in cm | Image distance (v) in cm | | --- | --- | --- | | 1 | -15 | -60 | | 2 | -25 | +100 | | 3 | -30 | +60 | | 4 | -40 | +40 | | 5 | -60 | +30 | | 6 | -100 | +25 | (a) Determine the focal length of the lens. Give reason for your answer. (b) Find the magnification of the image formed in observation number 3. (c) The numerical value of magnification is the same in the cases of observation numbers 1 and 2. List two differences between the images formed in these two cases.

   How the model answer begins

   1. (a) (i) The speed of light in A and B is the same. The speed of light in C is greater than in A and B.

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6. Q6Long answer5 marksAsked: 2025

   (A) (a) Observe the diagram given below and compare (i) the speed of light and (ii) the optical densities of these media, in the three media A, B and C. Also verify the answer of any one of these cases in terms of the refractive indices of these media. (b) Redraw the path of light in these three media for the situation in which a ray of light is incident on medium B from medium A (i) obliquely, and the optical density of medium B is more than the optical densities of A and C; and (ii) normally. Or (B) Analyse the observation table given below which shows the variation of image-distance (v) in cm with object-distance (u) in cm in the case of a convex lens, and answer the questions given below the table without carrying out any calculation: (a) Determine the focal length of the lens. Give reason for your answer. (b) Find the magnification of the image formed in observation number 3. (c) The numerical value of magnification is the same in the cases of observations number 1 and 2. List two differences between the images formed in these two cases.

7. Q7Long answer5 marksAsked: 2025

   (A) (a) Observe the following diagram and compare (i) speed of light and (ii) optical densities of the three media A, B and C. Also give justification for your answer of any one of the two cases in terms of refractive indices of A, B and C. (b) Redraw the path of a ray of light through the three media, if the ray of light starting from medium A falls on the medium B (i) Obliquely and the optical density of medium B is made more than that of A and C. (ii) The ray falls normally from medium A to medium B. (b) (B) Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations : (a) Determine the focal length of the lens. Give reason for your answer. (b) Find magnification of the image formed in Observation No. 3. (c) The numerical value of magnifications in cases of observation 1 and 2 is same. List two differences in the images formed in these two cases.

8. Q8Long answer5 marksAsked: 2024

   (a) (i) Draw a ray diagram to show the path of the refracted ray in each of the following cases : A ray of light incident on a concave lens (1) parallel to its principal axis, and (2) is directed towards its principal focus. (ii) A 4 cm tall object is placed perpendicular to the principal axis of convex lens of focal length 24 cm. The distance of object from the lens is 16 cm. Find the position and size of image formed. OR (b) (i) Draw a ray diagram to show the path of the reflected ray in each of the following cases : A ray of light incident on a convex mirror (1) parallel to its principal axis, and (2) is directed towards its principal focus.

9. Q9Long answer5 marksAsked: 2023

   (a) An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show the formation of the image. Write the value of magnification in this case. (b) A student has focussed the image of a candle flame on a white screen using a convex lens. The situation is as given below : Length of the flame = 2 cm Focal length of the lens = 12 cm Distance of the flame from the lens = 16 cm If the flame is perpendicular to the principal axis of the lens, calculate the values of the following : (i) Distance of the image from the lens (ii) Length of the image formed

   How the model answer begins

   1. (a) Ray diagram: object AB at 2F₁; a ray parallel to the axis refracts through F₂ and a ray through the optical centre goes straight; they meet at 2F₂, forming a real, inverted image of the same size.

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10. Q10Case-based4 marksAsked: 2023

    39. Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board held close to the mirror. Move the card-board back and forth gradually until you find a bright, sharp spot of light on the board. This spot of light is the image of the sun on the sheet of paper; which is also termed as "Principal Focus" of the concave mirror. (a) List two applications of concave mirror. (1) (b) If the distance between the mirror and the principal focus is 15 cm, find the radius of curvature of the mirror. (1) (c) Draw a ray diagram to show the type of image formed when an object is placed between pole and focus of a concave mirror. (2) OR (c) An object 10 cm in size is placed at 100 cm in front of a concave mirror. If its image is formed at the same point where the object is located, find : (i) focal length of the mirror, and (2) (ii) magnification of the image formed with sign as per Cartesian sign convention.

    How the model answer begins

    1. (a) As reflectors in torches, searchlights and vehicle headlights, to get a powerful parallel beam of light.

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11. Q11Case-based4 marksAsked: 2026

    38. Read the following passage and answer the questions given below : Lenses can form different types of images depending upon their focal length and position of object. A convex lens can create real, inverted or virtual, erect images, while a concave lens forms only virtual and diminished images. The focal length determines the power of lens. Convex lenses have positive focal length while concave lenses have negative focal length by convention. When lenses are placed together, their combined power is determined by the sum of their individual powers. Ray diagrams help to visualize how light converges or diverges through lens to form an image. (a) A convex lens of focal length 20 cm is used to form an image. If an object is placed at 40 cm from the lens, what will be the position and nature of image? (b) Illustrate the formation of image with the help of ray diagram, when the object is placed between the optical centre and principal focus of concave lens. (c) (i) A lens combination consists of a convex lens of focal length 30 cm and a concave lens of focal length 15 cm placed together. Find the equivalent focal length and power of this lens combination. OR (c) (ii) Two lenses are placed in contact. One is a concave lens of focal length 2 m and the other is a convex lens of focal length 1.5 m. How will this combination behave as a lens (convex or concave)? Give reason.

    How the model answer begins

    1. (a) 1/v − 1/u = 1/f with u = −40 cm and f = +20 cm gives v = +40 cm: the image is 40 cm on the other side of the lens (at 2F₂).

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12. Q12Long answer4 marksAsked: 2026

    The above ray diagram is to show image formation by a reflecting telescope. Reflecting telescope revolutionized our way of looking into the sky. Reflecting telescopes employ large mirrors to gather and focus light rather than relying solely on lenses as we do in the refracting telescopes. These telescopes utilize precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where the telescope forms an image for observation. (a) What kind of image of a star is seen by the observer in the eye-piece ? (b) What kind of mirror is used in this reflecting telescope ? (c) Explain with the reason, what kind of optical device (type of lens or mirror) is used at the eye-piece. OR (c) What is the role of plane mirror in image formation by this telescope ?

    How the model answer begins

    1. (a) In the eye-piece, the observer sees a real and magnified image of the star.

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13. Q13Case-based4 marksAsked: 2024

    39. Study the data given below in which focal length and relative distance of the object placed in front of three concave mirrors A, B and C are given : Case | Mirror | Focal length (cm) | Object-distance (cm) 1 | A | 20 | 45 2 | B | 15 | 30 3 | C | 30 | 20 (i) In which of the above cases will the size of the image formed by the mirror be smaller than the size of the object? Justify your answer. (ii) List two properties of the image formed in case 2. (iii) (A) What is the nature and size of the image formed by mirror C? Draw a ray diagram to justify your answer. OR (iii) (B) An object is placed at a distance of 18 cm from the pole of a concave mirror of focal length 12 cm. Find the position of the image in this case.

    How the model answer begins

    1. (i) The image is smaller than the object in Case 1, which is mirror A.

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14. Q14Case-based4 marksAsked: 2023

    The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density. On comparing two media, the one with the large refractive index is optically denser medium than the other. The other medium with a lower refractive index is optically rarer. Also the speed of light through a given medium is inversely proportional to its optical density. (i) Determine the speed of light in diamond if the refractive index of diamond with respect to vacuum is 2.42. Speed of light in vacuum is 3x10^8 m/s. (ii) Refractive indices of glass, water and carbon disulphide are 1.5, 1.33 and 1.62 respectively. If a ray of light is incident in these media at the same angle (say theta), then write the increasing order of the angle of refraction in these media. (iii) (A) The speed of light in glass is 2x10^8 m/s and in water is 2.25x10^8 m/s. (a) Which one of the two is optically denser and why ? (b) A ray of light is incident normally at the water-glass interface when it enters a thick glass container filled with water. What will happen to the path of the ray after entering the glass ? Give reason. OR (iii) (B) The absolute refractive indices of water and glass are 4/3 and 3/2 respectively. If the speed of light in glass is 2x10^8 m/s, find the speed of light in (i) vacuum and (ii) water.

    How the model answer begins

    1. (i) Given: refractive index of diamond with respect to vacuum, n = 2.42; speed of light in vacuum, c = 3 × 10^8 m/s. Formula: n = c/v, so v = c/n Substitution: v = (3 × 10^8 m/s) / 2.42 Calculation: v = 1.24 × 10^8 m/s…

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15. Q15Case-based4 marksAsked: 2026

    Read the following passage and answer the questions given below: Lenses can form different types of images depending on their focal length and the position of the object. A convex lens forms real, inverted or virtual, erect images while a concave lens always forms virtual and diminished images. The focal length determines the power of a lens. By convention, the focal length of a convex lens is positive while the focal length of a concave lens is negative. When lenses are placed in contact with each other, their total power is determined by the sum of the individual powers of the lenses. Ray diagrams help in showing how light converges or diverges through a lens to form images. (a) A convex lens of focal length 20 cm is used to form an image. If an object is placed at a distance of 40 cm from the lens, what will be the position and nature of the image? (b) With the help of a ray diagram, show the formation of image in the situation when the object is placed between the principal focus and the optical centre of a concave lens. (c) (i) In a lens combination, a convex lens of focal length 30 cm and a concave lens of focal length 15 cm are placed together in contact. Find the equivalent focal length and power of this combination. or (c) (ii) Two lenses are placed in contact. One is a concave lens of focal length 2 m and the other is a convex lens of focal length 1.5 m. What type of lens (convex or concave) will this combination behave as? Give reason.

    How the model answer begins

    1. (a) 1/v − 1/u = 1/f with u = −40 cm and f = +20 cm: 1/v = 1/20 − 1/40 = 1/40, so v = +40 cm — the image is 40 cm on the other side of the lens (at 2F₂).

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16. Q16Case-based4 marksAsked: 2024

    39. A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors - plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface. (a) Define the principal axis of a concave mirror. (b) A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of 10 cm from the pole of the mirror, find the radius of curvature of the mirror. (c) (i) An object is placed at a distance of 10 cm from the pole of a convex mirror of focal length 15 cm. Find the position of the image. OR (c) (ii) A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case.

17. Q17Case-based4 marksAsked: 2023

    Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses P1, P2, P3 ... as P = P1 + P2 + P3 ... This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses. (a) What is the nature (convergent / divergent) of the combination of a convex lens of power + 4 D and a concave lens of power - 2 D ? (b) Calculate the focal length of a lens of power - 2.5 D. (c) Draw a ray diagram to show the nature and position of an image formed by a convex lens of power + 0.1 D, when an object is placed at a distance of 20 cm from its optical centre. OR (c) How is a virtual image formed by a convex lens different from that formed by a concave lens ? Under what conditions do a convex and a concave lens form virtual images ?

18. Q18Short answer3 marksAsked: 2023

    (a) Complete the following ray diagram to show the formation of image : (b) Mention the nature, position and size of the image formed in this case. (c) State the sign of the image distance in this case using the Cartesian sign convention.

    How the model answer begins

    1. The ray diagram shows the object placed at the centre of curvature of the concave mirror. A ray of light from the top of the object, parallel to the principal axis, after reflection, passes through the principal focus…

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19. Q19Short answer3 marksAsked: 2026

    (a) Observe the given ray diagram and compare : (i) the speed of light in medium A and the speed of light in medium B. (ii) the optical densities of medium B and medium C. (b) Draw a ray diagram for refraction where the optical density of medium 'A' becomes equal to the optical density of medium 'C' and optical density of medium 'B' is greater than the optical density of medium 'A' and medium 'C'.

20. Q20Short answer3 marksAsked: 2025

    If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length 18 cm, where should the object be placed? Use mirror formula to determine the object distance for an image of magnification +2 produced by this mirror to justify your answer.

    How the model answer begins

    1. To get a virtual and magnified image, the object should be placed between P and F of the concave mirror, that is, between the pole and the principal focus, at a distance of less than 18 cm from the mirror. Then the…

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37 more questions of this chapter, each with its model answer, in the Ask Medha app.

Objective questions with the board’s key (10)

1. 1. CBSE 2026

   A convex lens of focal length 15 cm forms a real image. If the size of the image is equal to the size of the object, then the position of the object and the position of the image will be respectively :

   • (A) at - 15 cm and at - 15 cm from the lens
   • (B) at - 15 cm and at + 15 cm from the lens
   • (C) at - 30 cm and at + 30 cm from the lens ✓
   • (D) at - 30 cm and at - 30 cm from the lens

   Answer: (C)

2. 2. CBSE 2026

   From the following options choose the one which gives negative magnification greater than one :

   • (A) Concave mirror; Nature of image – real ✓
   • (B) Concave mirror; Nature of image – virtual
   • (C) Convex mirror; Nature of image – real
   • (D) Convex mirror; Nature of image – virtual

   Answer: (A)

3. 3. CBSE 2026

   Rays from the sun converge at a point 25 cm behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is :

   • (A) 20 cm ✓
   • (B) 40 cm
   • (C) 50 cm
   • (D) More than 50 cm

   Answer: (A)

4. 4. CBSE 2025

   To get an image of magnification -1 on a screen using a lens of focal length 20 cm, the object distance must be :

   • (A) Less than 20 cm
   • (B) 30 cm
   • (C) 40 cm ✓
   • (D) 80 cm

   Answer: (C)

5. 5. CBSE 2025

   An optical device 'X' is placed obliquely in the path of a narrow parallel beam of light. If the emergent beam gets displaced laterally, the device 'X' is :

   • (A) plane mirror
   • (B) convex lens
   • (C) glass slab ✓
   • (D) glass prism

   Answer: (C)

6. 6. CBSE 2025

   Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown :

   • (A)
   • (B)
   • (C) ✓
   • (D)

   Answer: (C)

7. 7. CBSE 2025

   Mirror 'X' is used to concentrate sunlight in solar furnace and Mirror 'Y' is fitted on the side of the vehicle to see the traffic behind the driver. Which of the following statements are true for the two mirrors ? (i) The image formed by mirror 'X' is real, diminished and at its focus. (ii) The image formed by mirror 'Y' is virtual, diminished and erect. (iii) The image formed by mirror 'X' is virtual, diminished and erect. (iv) The image formed by mirror 'Y' is real, diminished and at its focus.

   • (A) (i) and (ii) ✓
   • (B) (ii) and (iii)
   • (C) (iii) and (iv)
   • (D) (i) and (iv)

   Answer: (A)

8. 8. CBSE 2025

   If the absolute refractive indices of two media X and Y are 6/5 and 4/3 respectively, then the refractive index of Y with respect to X will be :

   • (A) 10/9 ✓
   • (B) 9/10
   • (C) 9/8
   • (D) 8/9

   Answer: (A)

9. 9. CBSE 2025

   In the given figure the angle of incidence and the angle of deviation respectively are :

   • (A) 1 and 5
   • (B) 7 and 6
   • (C) 7 and 4
   • (D) 1 and 6 ✓

   Answer: (D)

10. 10. CBSE 2025

    An object is placed at a distance of 30 cm from the pole of a concave mirror. If its real and inverted image is formed at 60 cm in front of the mirror, the focal length of the mirror is :

    • (A) - 15 cm
    • (B) - 20 cm ✓
    • (C) + 20 cm
    • (D) + 15 cm

    Answer: (B)

Questions parents and students ask

How many marks does "Light – Reflection and Refraction" carry in CBSE Class 10 Science?

In the CBSE papers of 2023–2026, this chapter carried about 7 marks and about 3 questions a year; by marks it ranks 3 in Science.

Which are the most important (VVI) questions of "Light – Reflection and Refraction"?

The 20 questions above are from the board’s real papers, each with the years it was asked; the most-asked come first with their full model answers. All 57 written questions of this chapter, with answers, are in the Ask Medha app.

Do the answers follow the board’s marking scheme?

Yes. CBSE publishes its marking schemes; every model answer here is written point by point to the marks the board’s own scheme gives, and checked by a second, independent model.