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Light — Reflection and Refraction

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Chapter Notes

Overview
This chapter explores the fundamental properties of light, focusing on reflection and refraction. It explains how light travels in straight lines and how it behaves when it encounters mirrors and lenses. The big idea is that by understanding the laws of reflection and refraction, we can predict and calculate the position, nature, and size of images formed by spherical mirrors and lenses, which has practical applications in everyday life like rear-view mirrors and magnifying glasses.
Key Concepts (28)
Reflection of light
The phenomenon of bouncing back of light from a polished surface into the same medium.
e.g. Seeing your face in a plane mirror.
Laws of reflection
(i) The angle of incidence is equal to the angle of reflection. (ii) The incident ray, the normal to the mirror at the point of incidence, and the reflected ray, all lie in the same plane.
e.g. When a light ray strikes a plane mirror at 30°, it reflects at 30° in the same plane.
Spherical mirror
A mirror whose reflecting surface is a part of a hollow sphere of glass.
e.g. A shining spoon's curved surface acts as a spherical mirror.
Concave mirror
A spherical mirror whose reflecting surface is curved inwards, i.e., faces towards the centre of the sphere.
e.g. The inner surface of a spoon.
Convex mirror
A spherical mirror whose reflecting surface is curved outwards.
e.g. The outer surface of a spoon.
Pole (P)
The centre of the reflecting surface of a spherical mirror. It lies on the surface of the mirror.
e.g. The midpoint of a concave mirror's surface.
Centre of curvature (C)
The centre of the sphere of which the reflecting surface of a spherical mirror forms a part. It is not a part of the mirror.
e.g. For a concave mirror, C lies in front of it; for a convex mirror, C lies behind it.
Radius of curvature (R)
The radius of the sphere of which the reflecting surface of a spherical mirror forms a part.
e.g. The distance from the pole to the centre of curvature.
Principal axis
An imaginary straight line passing through the pole and the centre of curvature of a spherical mirror.
e.g. The line joining P and C.
Principal focus (F)
For a concave mirror, it is the point on the principal axis where rays parallel to the principal axis converge after reflection. For a convex mirror, it is the point from which rays parallel to the principal axis appear to diverge after reflection.
e.g. The point where sunlight is concentrated by a concave mirror to burn paper.
Focal length (f)
The distance between the pole and the principal focus of a spherical mirror.
e.g. For a mirror with R = 20 cm, f = 10 cm.
Aperture
The diameter of the reflecting surface of a spherical mirror.
e.g. The width of the mirror from edge to edge.
Real image
An image that can be obtained on a screen, formed by actual intersection of light rays. It is always inverted.
e.g. The image of a candle flame on a screen placed in front of a concave mirror.
Virtual image
An image that cannot be obtained on a screen, formed by apparent intersection of light rays. It is always erect.
e.g. The image of your face in a plane mirror.
New Cartesian Sign Convention
A set of rules for assigning signs to distances in mirror and lens formulas: (i) object is placed to the left of the mirror/lens; (ii) distances measured from pole/optical centre to the right are positive, to the left are negative; (iii) distances measured perpendicular and above the principal axis are positive, below are negative.
e.g. For a concave mirror, u (object distance) is always negative, f is negative.
Mirror formula
The relationship between object distance (u), image distance (v), and focal length (f) of a spherical mirror: 1/v + 1/u = 1/f.
e.g. Used to calculate v when u and f are known.
Magnification (m)
The ratio of the height of the image to the height of the object. It is also given by m = -v/u.
e.g. If m = +0.23, the image is virtual, erect, and smaller.
Refraction of light
The phenomenon of change in direction of light when it travels obliquely from one transparent medium to another.
e.g. A pencil appearing bent when partly immersed in water.
Laws of refraction (Snell's law)
(i) The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane. (ii) 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: sin i / sin r = constant.
e.g. Light entering water from air bends towards the normal.
Refractive index (n)
The ratio of the speed of light in a given pair of media. Absolute refractive index of a medium is the ratio of speed of light in vacuum/air to the speed of light in that medium: n = c/v.
e.g. Refractive index of water is 1.33, meaning light travels 1.33 times faster in air than in water.
Optically denser medium
A medium with a higher refractive index, in which light travels slower and bends towards the normal when entering from a rarer medium.
e.g. Glass (n=1.52) is optically denser than water (n=1.33).
Optically rarer medium
A medium with a lower refractive index, in which light travels faster and bends away from the normal when entering from a denser medium.
e.g. Air is optically rarer than water.
Lens
A transparent material bound by two surfaces, of which one or both surfaces are spherical.
e.g. The magnifying glass used by watchmakers.
Convex lens (converging lens)
A lens that is thicker at the middle than at the edges, and converges light rays to a point.
e.g. The lens in a magnifying glass.
Concave lens (diverging lens)
A lens that is thicker at the edges than at the middle, and diverges light rays.
e.g. The lens used in some spectacles to correct myopia.
Optical centre (O)
The central point of a lens. A ray of light passing through the optical centre goes without any deviation.
e.g. The midpoint of a convex lens.
Principal focus of a lens
For a convex lens, it is the point on the principal axis where rays parallel to the principal axis converge after refraction. For a concave lens, it is the point from which rays parallel to the principal axis appear to diverge after refraction.
e.g. The point where sunlight is focused by a convex lens to burn paper.
Focal length of a lens
The distance between the optical centre and the principal focus of a lens.
e.g. The distance from the lens to the sharp image of the Sun on paper.
Formulas & Equations (6)
R = 2f
Reads as: Radius of curvature equals twice the focal length
Variables: R = radius of curvature (in metres or cm), f = focal length (in same unit)
Use when: To find focal length from radius of curvature or vice versa for spherical mirrors of small aperture.
⚠ Students forget that this relation is valid only for spherical mirrors with small aperture, and they often use it for lenses.
1/v + 1/u = 1/f
Reads as: One upon v plus one upon u equals one upon f
Variables: v = image distance from pole (in m or cm), u = object distance from pole (in m or cm), f = focal length (in same unit)
Use when: To find the position of the image (v) when object distance (u) and focal length (f) are known, or to find f when u and v are known.
⚠ Students forget to apply the New Cartesian Sign Convention correctly, especially the signs for u, v, and f for concave and convex mirrors.
m = h'/h = -v/u
Reads as: Magnification equals h dash upon h equals negative v upon u
Variables: m = magnification (no unit), h' = height of image (in m or cm), h = height of object (in m or cm), v = image distance, u = object distance
Use when: To find the size and nature of the image (real/virtual, erect/inverted) from object and image distances.
⚠ Students often forget that a negative m indicates a real and inverted image, while a positive m indicates a virtual and erect image.
n21 = v1/v2
Reads as: Refractive index of medium 2 with respect to medium 1 equals speed of light in medium 1 divided by speed of light in medium 2
Variables: n21 = refractive index of medium 2 relative to medium 1 (no unit), v1 = speed of light in medium 1 (m/s), v2 = speed of light in medium 2 (m/s)
Use when: To calculate the relative refractive index between two media when their speeds of light are known.
⚠ Students confuse which speed goes in the numerator; remember it is speed in the first medium divided by speed in the second medium.
nm = c/v
Reads as: Absolute refractive index of a medium equals speed of light in vacuum divided by speed of light in the medium
Variables: nm = absolute refractive index of the medium (no unit), c = speed of light in vacuum/air (3 × 10^8 m/s), v = speed of light in the medium (m/s)
Use when: To find the refractive index of a medium when the speed of light in it is known, or to find the speed of light in a medium when its refractive index is known.
⚠ Students often use the speed of light in air instead of vacuum; for board exams, treat c as 3 × 10^8 m/s in air.
sin i / sin r = constant (n21)
Reads as: Sine of angle of incidence divided by sine of angle of refraction equals a constant
Variables: i = angle of incidence (degrees), r = angle of refraction (degrees), constant = refractive index of second medium with respect to first (n21)
Use when: To find the angle of refraction when angle of incidence and refractive index are known, or to find refractive index from angles.
⚠ Students forget that this law applies only for a given pair of media and for a given colour of light.
How It Works
Image formation by a concave mirror
  1. Step 1: Draw the principal axis and mark the pole (P), focus (F), and centre of curvature (C) on it.
  2. Step 2: Place the object at a given position (e.g., beyond C, at C, between C and F, at F, between P and F).
  3. Step 3: Draw at least two of the following rays from the top of the object: (i) a ray parallel to the principal axis, which after reflection passes through F; (ii) a ray passing through F, which after reflection becomes parallel to the principal axis; (iii) a ray passing through C, which reflects back along the same path.
  4. Step 4: The point where the reflected rays (or their extensions) intersect gives the position of the image.
  5. Step 5: Determine the nature (real/virtual), position, and size (diminished/enlarged/same) of the image from the ray diagram.
💡 For a concave mirror, when the object is between P and F, the image is virtual, erect, and enlarged, and is formed behind the mirror.
Image formation by a convex mirror
  1. Step 1: Draw the principal axis and mark P, F, and C behind the mirror.
  2. Step 2: Place the object at a given position (at infinity or between infinity and P).
  3. Step 3: Draw two rays from the top of the object: (i) a ray parallel to the principal axis, which after reflection appears to diverge from F; (ii) a ray directed towards C, which reflects back along the same path.
  4. Step 4: Extend the reflected rays backward (behind the mirror) to find the point where they appear to meet.
  5. Step 5: The image is always virtual, erect, and diminished, and lies between P and F behind the mirror.
💡 Convex mirrors always produce a virtual, erect, and diminished image, regardless of the object's position.
Refraction through a rectangular glass slab
  1. Step 1: A ray of light (incident ray) strikes the first surface (air-glass interface) at an angle.
  2. Step 2: At the point of incidence, the ray bends towards the normal because it enters a denser medium (glass).
  3. Step 3: The ray travels through the glass slab and strikes the second surface (glass-air interface).
  4. Step 4: At the second surface, the ray bends away from the normal because it enters a rarer medium (air).
  5. Step 5: The emergent ray is parallel to the incident ray but is laterally shifted.
💡 The emergent ray is parallel to the incident ray because the bending at the two opposite parallel faces is equal and opposite.
Image formation by a convex lens
  1. Step 1: Draw the principal axis and mark the optical centre (O), and the two foci (F1 and F2) on either side.
  2. Step 2: Place the object at a given position (e.g., beyond 2F1, at 2F1, between F1 and 2F1, at F1, between F1 and O).
  3. Step 3: Draw at least two rays from the top of the object: (i) a ray parallel to the principal axis, which after refraction passes through F2; (ii) a ray passing through the optical centre O, which goes straight without deviation; (iii) a ray passing through F1, which after refraction becomes parallel to the principal axis.
  4. Step 4: The point where the refracted rays intersect gives the position of the image.
  5. Step 5: Determine the nature (real/virtual), position, and size of the image.
💡 For a convex lens, when the object is between F1 and O, the image is virtual, erect, and enlarged, and is formed on the same side as the object.
Image formation by a concave lens
  1. Step 1: Draw the principal axis and mark O, and the two foci (F1 and F2) on either side.
  2. Step 2: Place the object at any position (at infinity or between infinity and O).
  3. Step 3: Draw two rays from the top of the object: (i) a ray parallel to the principal axis, which after refraction appears to diverge from F1; (ii) a ray passing through the optical centre O, which goes straight without deviation.
  4. Step 4: Extend the refracted rays backward to find the point where they appear to meet.
  5. Step 5: The image is always virtual, erect, and diminished, and lies between O and F1 on the same side as the object.
💡 Concave lenses always produce a virtual, erect, and diminished image, regardless of the object's position.
Exam Traps — Don't Make These Mistakes
⚠ Sign convention for concave mirror focal length
✗ f = +15 cm for a concave mirror
→ According to the New Cartesian Sign Convention, distances measured to the left of the pole (against the incident light) are negative. Since the focus of a concave mirror is in front of the mirror (to the left), f must be negative.
✓ f = -15 cm for a concave mirror
⚠ Nature of image for object at C in concave mirror
✗ The image is virtual and erect when the object is at C.
→ When the object is at the centre of curvature (C) of a concave mirror, the image is formed at C itself, and it is real and inverted, of the same size as the object.
✓ The image is real, inverted, and of the same size as the object, formed at C.
⚠ Magnification sign for virtual image
✗ Magnification m = -2 for a virtual image.
→ A negative magnification indicates a real and inverted image. For a virtual and erect image, the magnification is positive.
✓ Magnification m = +2 for a virtual and erect image.
⚠ Refractive index and speed of light
✗ Higher refractive index means light travels faster in that medium.
→ Refractive index n = c/v, so a higher n means a lower speed of light (v) in that medium.
✓ Higher refractive index means light travels slower in that medium.
⚠ Bending of light during refraction
✗ Light always bends towards the normal when entering any other medium.
→ Light bends towards the normal only when entering a denser medium (higher refractive index). When entering a rarer medium, it bends away from the normal.
✓ Light bends towards the normal when entering a denser medium and away from the normal when entering a rarer medium.
⚠ Principal focus of convex mirror
✗ The principal focus of a convex mirror is a point in front of the mirror where parallel rays converge.
→ For a convex mirror, parallel rays appear to diverge from a point behind the mirror. The principal focus is behind the mirror, not in front.
✓ The principal focus of a convex mirror is a point on the principal axis behind the mirror from which parallel rays appear to diverge after reflection.
Compare & Contrast
Nature of image for an object placed between P and F
Concave mirror
Convex mirror
A concave mirror produces a virtual, erect, and enlarged image, while a convex mirror always produces a virtual, erect, and diminished image regardless of object position.
Action on parallel rays
Convex lens
Concave lens
A convex lens converges parallel rays to a point (principal focus) on the other side, while a concave lens diverges parallel rays, making them appear to come from a point on the same side.
Ability to be obtained on a screen
Real image
Virtual image
A real image can be obtained on a screen because it is formed by actual intersection of light rays, while a virtual image cannot be obtained on a screen because it is formed by apparent intersection of light rays.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 SA-I (2 marks), 1 SA-II (3 marks), 1 LA (5 marks) — total 12 marks
Most asked: Mirror formula and magnification numericals · Sign convention for spherical mirrors · Image formation by concave and convex mirrors (ray diagrams and table) · Laws of reflection and refraction · Refractive index numericals · Image formation by convex and concave lenses (ray diagrams and table)
Don't skip: Numerical problems using mirror formula and magnification; Ray diagrams for image formation by concave mirror and convex lens; Snell's law and refractive index calculations
One-Line Revision (read aloud before the exam)
  1. Laws of reflection: angle of incidence equals angle of reflection, and all three rays lie in the same plane.
  2. For a spherical mirror, R = 2f, and the principal focus lies midway between the pole and centre of curvature.
  3. Concave mirrors can form both real and virtual images; convex mirrors always form virtual, erect, and diminished images.
  4. Convex mirrors are used as rear-view mirrors in vehicles because they give a wider field of view and always produce an erect image.
  5. New Cartesian Sign Convention: object is placed to the left, distances to the right are positive, to the left are negative.
  6. Mirror formula: 1/v + 1/u = 1/f, where u is always negative for real objects.
  7. Magnification m = h'/h = -v/u; negative m means real and inverted image, positive m means virtual and erect image.
  8. Refraction is the bending of light when it travels obliquely from one transparent medium to another.
  9. Snell's law: sin i / sin r = constant (refractive index of second medium with respect to first).
  10. Absolute refractive index n = c/v, where c = 3 × 10^8 m/s in vacuum.
  11. Light bends towards the normal when entering a denser medium and away from the normal when entering a rarer medium.
  12. Convex lenses converge light and can form both real and virtual images; concave lenses diverge light and always form virtual, erect, and diminished images.
  13. A ray passing through the optical centre of a lens goes undeviated.
  14. The emergent ray through a rectangular glass slab is parallel to the incident ray but laterally displaced.

MCQs — 10 Questions with Answers

Q1. A student performs Activity 9.2 with a concave mirror and focuses sunlight onto a paper sheet, creating a small bright spot. If the student moves the paper further away from the mirror, what will happen to the bright spot?

  • A. The spot will disappear because the light rays are diverging after the focal point
  • B. The spot will become larger and dimmer because the reflected rays diverge after the focal point ✓
  • C. The spot will become larger and brighter
  • D. The spot will move to the side of the paper

Answer: B — When paper is moved beyond the focal point of a concave mirror, the reflected rays begin to diverge. The spot does not disappear; it becomes larger and dimmer (unfocused). Disappearance (option A) is incorrect; the light is still there but spread over a larger area.

Q2. A person stands 25 cm in front of a large concave mirror with a radius of curvature of 100 cm. Based on the relationship between object distance and focal length, where will the image form?

  • A. Between the pole and the focal point (real, inverted, magnified)
  • B. At the centre of curvature (real, inverted, same size)
  • C. Beyond the centre of curvature (real, inverted, diminished)
  • D. Behind the mirror (virtual, erect, magnified) ✓

Answer: D — With radius of curvature 100 cm, focal length f = 50 cm. The object is at u = 25 cm, which is less than f (object between pole and focal point). Using 1/v = 1/f - 1/u = 1/50 - 1/25 = -1/50, so v = -50 cm. The negative sign indicates the image is behind the mirror (virtual, erect, and magnified). Option A is wrong (real images need u > f), B and C require u beyond focal point.

Q3. A convex mirror is installed on a road curve as a safety mirror. A car approaching the mirror appears smaller than its actual size. Why does the convex mirror provide a wider field of view compared to a plane mirror?

  • A. Convex mirrors diverge light rays, allowing images of objects spread over a larger angular range to be visible ✓
  • B. Convex mirrors have a larger physical size than plane mirrors
  • C. Convex mirrors reflect light at steeper angles than plane mirrors
  • D. Convex mirrors form virtual images that extend beyond the mirror's surface

Answer: A — The diverging nature of convex mirrors creates virtual images of a wider area; option B is false as size is arbitrary, and option C misunderstands the law of reflection which applies equally to all surfaces.

Q4. A student observes that when she looks at her face in the inner (concave) surface of a shining spoon held close to her face, the image appears upright and magnified. When she moves the spoon away slowly, at what point does the image suddenly invert and become real?

  • A. When the object distance equals the radius of curvature
  • B. When the object distance equals the focal length ✓
  • C. When the object distance is between the focal length and the centre of curvature
  • D. When the object distance exceeds the centre of curvature

Answer: B — At the focal point (u = f), the image forms at infinity; beyond this point (u < f), the image becomes real and inverted; option A is incorrect as the image inverts before reaching the center of curvature.

Q5. During an experiment, a candle is placed 20 cm in front of a concave mirror of focal length 10 cm. A student calculates using the mirror formula and finds the image distance to be 20 cm. What type of image is formed and where?

  • A. Real, inverted, same size as object, at the centre of curvature ✓
  • B. Virtual, upright, magnified, behind the mirror
  • C. Real, inverted, diminished, beyond the centre of curvature
  • D. Real, inverted, magnified, between the focal point and pole

Answer: A — Using 1/f = 1/u + 1/v: 1/10 = 1/20 + 1/v gives v = 20 cm, placing the image at the centre of curvature with magnification m = 1, forming a real inverted image of equal size; option C is a common wrong application of mirror rules.

Q6. Assertion (A): When a concave mirror is used as a shaving mirror, it is held close to the face so that the face lies between the pole and the focal point. Reason (R): In this region, a concave mirror always forms a virtual, erect, and magnified image. Choose the correct option:

  • A. Both A and 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

Answer: A — Between P and F of a concave mirror, the image is always virtual, erect, and magnified, making it ideal for shaving; the reason correctly explains why this position is chosen.

Q7. Assertion (A): A convex mirror always forms a virtual image regardless of the object's position. Reason (R): The diverging nature of a convex mirror causes reflected rays to appear to originate from a point behind the mirror. Choose the correct option:

  • A. Both A and 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

Answer: A — Convex mirrors always diverge rays, creating virtual images at any object position; the reason correctly explains this behavior.

Q8. Assertion (A): The principal axis of a spherical mirror is perpendicular to the mirror's surface at the pole. Reason (R): The principal axis passes through both the pole and the centre of curvature of the mirror. Choose the correct option:

  • A. Both A and 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

Answer: B — Both statements are true: the principal axis is normal to the mirror at the pole and passes through P and C; however, reason R describes the definition of the principal axis rather than explaining why it is perpendicular.

Q9. In an experiment, a student places objects at different distances from a concave mirror and measures image distances. The student observes that as the object moves from the center of curvature toward the focal point, the image distance increases from equal to the object distance toward infinity. What does this observation reveal about the mirror?

  • A. The mirror obeys the mirror formula, and the image size increases as it moves away from the mirror ✓
  • B. The focal length of the mirror is increasing with object position
  • C. The mirror is defective because image distance should decrease
  • D. The radius of curvature is changing due to the mirror's properties

Answer: A — The mirror formula 1/f = 1/u + 1/v explains that as u decreases (object approaches F), v increases, consistent with the observation; option B wrongly suggests focal length changes, which is a property of the mirror itself.

Q10. A laboratory experiment involves comparing images formed by a plane mirror and a concave mirror when an object is placed 30 cm away. The student notes that the plane mirror shows a virtual image at 30 cm behind, while the concave mirror (f = 15 cm) shows a real, inverted image at 30 cm in front. What is the key difference in how these mirrors bend light paths?

  • A. The concave mirror converges light rays to form real images, while the plane mirror reflects rays parallel to maintain virtual image position ✓
  • B. The plane mirror absorbs more light, resulting in virtual images only
  • C. The concave mirror is more reflective than the plane mirror
  • D. The plane mirror reverses light direction while the concave mirror amplifies it

Answer: A — Concave mirrors converge rays toward the focal point to form real images for objects beyond F; plane mirrors reflect parallel rays creating virtual images; option B is incorrect as light absorption doesn't determine image type.

Flashcards

What is a ray of light?

A ray of light is a straight line representing the direction of light propagation from a source to an object.

State the laws of reflection of light.

The angle of incidence equals the angle of reflection, and the incident ray, reflected ray, and normal all lie in the same plane.

What is a spherical mirror?

A spherical mirror is a curved mirror whose reflecting surface forms part of a sphere, either concave (inward) or convex (outward).

Define the pole of a spherical mirror.

The pole (P) is the center point of the reflecting surface of a spherical mirror, lying on the surface itself.

What is the centre of curvature of a mirror?

The centre of curvature (C) is the center of the imaginary sphere of which the mirror's surface forms a part, located outside the mirror.

Define the radius of curvature.

The radius of curvature (R) is the radius of the sphere of which the reflecting surface forms a part, equal to the distance PC.

What is the principal axis of a mirror?

The principal axis is a straight line passing through the pole and centre of curvature of a spherical mirror, perpendicular to the mirror at the pole.

Where is the focus of a concave mirror formed?

The focus (F) of a concave mirror is the point on the principal axis where all light rays parallel to the axis converge after reflection.

How do concave and convex mirrors differ in position of centre of curvature?

In a concave mirror, the centre of curvature lies in front of the mirror, while in a convex mirror it lies behind the mirror.

What happens when you bring a concave mirror close to your face?

The image becomes magnified (enlarged) and remains upright and virtual when the object is between the pole and focus.

Important Board Questions

Define the following terms related to spherical mirrors: (a) Pole, (b) Centre of Curvature, (c) Radius of Curvature. [2 marks]

State the location and meaning of each term: Pole is center point on mirror surface (P), Centre of Curvature is center of the imaginary sphere (C, outside mirror), Radius of Curvature is the distance PC equal to R.

Explain with the help of a ray diagram why a concave mirror can concentrate sunlight at its focus. What is the relationship between focal length and radius of curvature? [3 marks]

Show that parallel rays incident on concave mirror converge at focus F after reflection (use law of reflection for each ray). State the relationship: f = R/2, meaning focal length equals half the radius of curvature because focus lies at midpoint between pole and centre of curvature.

Compare the images formed by a plane mirror, a concave mirror, and a convex mirror when an object is placed in front of them. Explain the differences in terms of the position of the centre of curvature and the type of image formed. How does the position of the object affect the image formed by a concave mirror? [5 marks]

For plane mirror: virtual, erect, same size, laterally inverted (no centre of curvature). For concave mirror: centre of curvature in front, can form real/virtual images depending on object position (beyond C → real diminished; at C → real same size; between C and F → real magnified; between F and P → virtual magnified). For convex mirror: centre of curvature behind, always forms virtual erect diminished image. Explain how changing object distance changes image nature in concave mirror using mirror formula and ray diagrams.

Assertion-Reason Questions for Light — Reflection and Refraction

Q1. Assertion (A):

A plane mirror always forms an image that is the same size as the object.

Reason (R):

The magnification produced by a plane mirror is always equal to 1.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true, and the reason directly explains why the image is the same size as the object. A magnification of 1 means no enlargement or reduction, resulting in equal-sized images.

Q2. Assertion (A):

The centre of curvature of a concave mirror lies in front of the mirror.

Reason (R):

The concave mirror's reflecting surface is curved inwards towards the centre of the sphere.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both statements are true, and the reason correctly explains the assertion. Since the reflecting surface curves inward, the centre of the sphere from which it's derived must be on the side of the curve, which is in front of the mirror.

Q3. Assertion (A):

Light undergoes diffraction when it encounters a very small opaque object.

Reason (R):

Diffraction occurs because light travels in perfectly straight lines.

Answer: C — A is true but R is false — The assertion is true—diffraction does occur around small obstacles. However, the reason is false. Diffraction occurs precisely because the straight-line approximation of light fails for small objects; light is not purely a straight-line phenomenon but also has wave properties.

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Case-Based Questions (CBQ) for Light — Reflection and Refraction

Case Study:

Ravi is conducting an experiment with a concave mirror of focal length 10 cm. He places a candle 30 cm away from the mirror's pole on the principal axis. He wants to observe the nature and characteristics of the image formed on a screen. The radius of curvature of his mirror is 20 cm. When he adjusts the screen position, he notices a real, inverted, and diminished image of the candle appears on the screen at a specific distance from the mirror.

Q1. What is the radius of curvature of Ravi's concave mirror?

  • A. 10 cm
  • B. 15 cm
  • C. 20 cm ✓
  • D. 30 cm

Answer: C

Q2. At what distance from the mirror is the object (candle) placed?

  • A. At the focal point
  • B. Between the focal point and centre of curvature
  • C. At the centre of curvature
  • D. Beyond the centre of curvature ✓

Answer: D

Q3. What is the nature of the image formed when the object is at 30 cm (beyond the centre of curvature)?

  • A. Virtual, erect, and magnified
  • B. Real, inverted, and diminished ✓
  • C. Virtual, inverted, and magnified
  • D. Real, erect, and magnified

Answer: B

Q4. If Ravi moves the candle closer to the mirror, what change will occur in the image?

  • A. The image will become more magnified and move away from the mirror ✓
  • B. The image will become smaller and move closer to the mirror
  • C. The image will become larger and move closer to the mirror
  • D. The image will disappear entirely

Answer: A

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Previous Year Questions (PYQ) for Light — Reflection and Refraction

Real CBSE board exam questions from past papers — free to attempt.

CBSE 2026 · Set 31/4/1 · 3 marks

(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'.

CBSE 2026 · Set 31/4/2 · 3 marks

[Diagram-based question — skipped] (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'.

CBSE 2026 · Set 31/4/2 · 4 marks

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?

CBSE 2026 · Set 31/4/3 · 3 marks

A mirror used for rear-view of an automobile has a focal length 2.0 m. If a car is located at 8.0 m from the mirror - (a) Find out the position of the image of this car as seen in the mirror. (b) Draw the ray-diagram for image formation by the rear-view mirror.

CBSE 2026 · Set 31/5/1 · 1 mark

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:

  • 20 cm
  • 40 cm
  • 50 cm
  • More than 50 cm

CBSE 2026 · Set 31/5/1 · 2 marks

(a) Relate the speed of light in the given medium with its optical density. (b) Using the information given in the table below, arrange the medium A, B and C in the ascending order of their optical density. Medium A: 2.25 × 10^8 m/s, Medium B: 2 × 10^8 m/s, Medium C: 2.08 × 10^8 m/s

CBSE 2026 · Set 31/5/1 · 3 marks

(a) Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change? Explain.

CBSE 2026 · Set 31/5/1 · 3 marks

(a) A ray of light after reflection from a concave mirror becomes parallel to its principal axis. Draw a labelled ray diagram to show this. (b) (i) Differentiate between the virtual images formed by a convex mirror and concave mirror. (ii) The value of magnification 'm' for a mirror is –2. Calculate the height of object if the height of image is 20 cm.

CBSE 2026 · Set 31/5/2 · 1 mark

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 :

  • 20 cm
  • 40 cm
  • 50 cm
  • More than 50 cm

CBSE 2026 · Set 31/5/2 · 2 marks

(a) Define absolute refractive index of an optical medium. (b) Material Medium | Refractive Index | A | 1.50 | B | 1.46 | C | 1.31 | D | 1.77 | Arrange these material mediums given in the table in increasing order of speed of light through them.

CBSE 2026 · Set 31/5/2 · 3 marks

An object is placed at a distance of 30 cm in front of a convex lens of focal length 15 cm. Use lens formula to determine the position of the image. What will be the size of the image in this case ?

CBSE 2026 · Set 31/5/2 · 3 marks

(a) Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change ? Explain.

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Class 10 Science Formula Sheet

Every formula and chemical equation from the 10 chapters on one page, checked against the NCERT textbook and the CBSE 2026-27 syllabus. Free PDF download.

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Class 10 Science Previous Year Questions, Chapter-wise

All 875 CBSE board questions from 2022–2026, sorted by chapter and question type. Free PDF download.

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