Class 10th Science Chapter 9 – Light – Reflection and Refraction | Reflection of Light

💡 Light – Reflection and Refraction | Reflection of Light

Class 10 Science | CBSE + Foundation + Competitive Level

🔦 Reflection of Light | प्रकाश का परावर्तन

1. What is Reflection of Light? | प्रकाश का परावर्तन क्या है?

Reflection of Light: जब प्रकाश की किरण किसी चमकीली या परावर्तक सतह पर गिरकर उसी माध्यम में वापस लौटती है, तो इस घटना को Reflection of Light (प्रकाश का परावर्तन) कहते हैं।

When a ray of light falls on a reflecting surface and returns into the same medium, the phenomenon is called reflection of light.

Examples / उदाहरण:

• Plane mirror / समतल दर्पण
• Polished metal surface / चमकीली धातु की सतह
• Calm water surface / शांत जल की सतह
• Glass mirror / काँच का दर्पण

2. Important Terms Related to Reflection

Term	English Meaning	Hindi Meaning
Incident Ray	Ray falling on the reflecting surface	आपतित किरण
Reflected Ray	Ray returning after reflection	परावर्तित किरण
Point of Incidence	Point where incident ray strikes the surface	आपतन बिंदु
Normal	Perpendicular drawn at point of incidence	अभिलम्ब
Angle of Incidence	Angle between incident ray and normal	आपतन कोण
Angle of Reflection	Angle between reflected ray and normal	परावर्तन कोण

3. Animated Diagram – Reflection of Light

4. Laws of Reflection | परावर्तन के नियम

First Law: The incident ray, reflected ray and normal at the point of incidence all lie in the same plane.

पहला नियम: आपतित किरण, परावर्तित किरण तथा आपतन बिंदु पर खींचा गया अभिलम्ब तीनों एक ही तल में होते हैं।

Second Law: The angle of incidence is equal to the angle of reflection.

दूसरा नियम: आपतन कोण परावर्तन कोण के बराबर होता है।

∠i = ∠r

Important: Angles of incidence and reflection are always measured from the normal, not from the mirror surface.
आपतन कोण और परावर्तन कोण हमेशा अभिलम्ब से मापे जाते हैं, दर्पण की सतह से नहीं।

5. Types of Reflection | परावर्तन के प्रकार

Regular Reflection	Diffuse Reflection
Occurs on smooth and polished surfaces.	Occurs on rough surfaces.
Reflected rays remain parallel.	Reflected rays scatter in different directions.
Clear image can be formed.	Generally no clear image is formed.
Example: Plane mirror.	Example: Wall, paper.

Golden Point: Diffuse reflection does not mean that laws of reflection are violated. Every individual ray still follows the laws of reflection.

6. Reflection from a Plane Mirror | समतल दर्पण से परावर्तन

A plane mirror has a flat reflecting surface.

समतल दर्पण की परावर्तक सतह समतल होती है।

Property	Plane Mirror Image
Nature	Virtual
Orientation	Erect
Size	Same as object
Position	Same distance behind mirror as object is in front
Laterally Inverted	Yes

7. Image Formation by Plane Mirror

8. Lateral Inversion | पार्श्व परिवर्तन

The left side of an object appears as the right side in its mirror image and vice versa. This phenomenon is called lateral inversion.

दर्पण में वस्तु का बायाँ भाग दायाँ तथा दायाँ भाग बायाँ दिखाई देता है। इसे पार्श्व परिवर्तन कहते हैं।

Object → Mirror → Laterally Inverted Image

Example: The word AMBULANCE is written laterally inverted on the front of ambulances so that drivers can read it correctly in their rear-view mirrors.

9. Real Image vs Virtual Image

Real Image	Virtual Image
Actually formed by convergence of rays.	Appears to be formed by apparent intersection of rays.
Can generally be obtained on a screen.	Cannot be obtained on a screen.
Usually inverted in common mirror/lens cases.	Usually erect in plane mirror.

10. Multiple Reflection | बहु-परावर्तन

When light undergoes reflection repeatedly from more than one reflecting surface, it is called multiple reflection.

जब प्रकाश एक से अधिक परावर्तक सतहों से बार-बार परावर्तित होता है, तो इसे बहु-परावर्तन कहते हैं।

Applications:

• Periscope
• Kaleidoscope
• Multiple images between mirrors
• Decorative mirrors

11. Reflection Between Two Plane Mirrors

When two plane mirrors are placed at an angle, multiple images of an object can be formed. For certain angles, the number of images can be calculated using:

n = 360° / θ − 1

यह सूत्र उन सामान्य स्थितियों में उपयोगी है जहाँ 360°/θ पूर्णांक है और वस्तु उपयुक्त रूप से स्थित है।

Example: If two mirrors are placed at 90°:
n = 360/90 − 1 = 4 − 1 = 3 images

12. Introduction to Spherical Mirrors

A spherical mirror is a part of a hollow sphere whose one surface is polished. There are two main types:

Concave Mirror Convex Mirror

Concave Mirror	Convex Mirror
Reflecting surface curves inward.	Reflecting surface bulges outward.
Converging mirror.	Diverging mirror.
Can form real or virtual images depending on object position.	Forms virtual, erect and diminished image for a real object.

13. Important Terms of Spherical Mirrors

Term	Meaning
Pole (P)	Centre of the reflecting surface of the mirror.
Centre of Curvature (C)	Centre of the sphere of which the mirror is a part.
Radius of Curvature (R)	Distance between P and C.
Principal Axis	Straight line passing through P and C.
Principal Focus (F)	Point where parallel rays converge or appear to diverge.
Focal Length (f)	Distance between P and F.

R = 2f

Competitive Point: For a spherical mirror under the paraxial approximation, the principal focus lies approximately midway between P and C.

14. Important Rays for Spherical Mirrors

Ray 1: A ray parallel to principal axis is reflected through F in a concave mirror.

Ray 2: A ray passing through F is reflected parallel to principal axis.

Ray 3: A ray passing through C retraces its path after reflection.

Ray 4: In a convex mirror, a parallel ray appears to come from F behind the mirror.

15. Mirror Formula

1/f = 1/v + 1/u

Where:

• f = focal length
• u = object distance
• v = image distance

Sign Convention: Class 10 numerical problems involving spherical mirrors use the New Cartesian Sign Convention.

• All distances are measured from the pole.
• Distances measured in the direction of incident light are positive.
• Distances measured opposite to the direction of incident light are negative.
• Heights above the principal axis are positive.
• Heights below the principal axis are negative.

16. Magnification of Spherical Mirror

m = hᵢ / hₒ = −v/u

Magnification	Meaning
m > 1	Magnified image
m = 1	Same size
m < 1	Diminished image
m positive	Erect image
m negative	Inverted image

17. Image Formation by Concave Mirror

Object Position	Image Position	Nature	Size
Beyond C	Between F and C	Real, inverted	Diminished
At C	At C	Real, inverted	Same size
Between C and F	Beyond C	Real, inverted	Magnified
At F	At infinity	Real, inverted	Highly enlarged
Between F and P	Behind mirror	Virtual, erect	Magnified

18. Image Formation by Convex Mirror

For a real object placed anywhere in front of a convex mirror, the image is:

• Virtual
• Erect
• Diminished
• Formed behind the mirror between P and F

Major Application: Convex mirrors are used as rear-view mirrors in vehicles because they provide a wider field of view.

19. Applications of Reflection of Light

Application	Reason
Rear-view mirror	Convex mirror gives wider field of view.
Shaving mirror	Concave mirror can produce enlarged erect image when face is within focal length.
Searchlight	Concave reflector produces a nearly parallel beam when source is near focus.
Solar furnace	Concave mirror concentrates sunlight.
Headlights	Concave reflector helps direct light into a beam.
Periscope	Uses reflection from mirrors/prisms to change direction of light.

20. Reflection in Daily Life

• We see our face in a mirror due to reflection.
• Objects are visible because light reflected from them enters our eyes.
• Moon is visible because it reflects sunlight.
• Road signs are designed to reflect light efficiently.
• Rear-view mirrors use convex mirrors.

21. Reflection vs Refraction

Reflection	Refraction
Light returns into the same medium.	Light enters another transparent medium and changes speed/direction.
Occurs at reflecting surface.	Occurs at interface between transparent media.
∠i = ∠r	n₁ sin i = n₂ sin r

22. Important Formula Sheet

∠i = ∠r

R = 2f

1/f = 1/v + 1/u

m = hᵢ/hₒ = −v/u

n = 360°/θ − 1

23. 30 MCQs | Multiple Choice Questions

Q1. Reflection of light means:

A. Return of light into the same medium

B. Bending of light only

C. Absorption of light

D. Splitting of light

Answer: A

Reflection occurs when light returns into the same medium after striking a surface.

Q2. The angle of reflection is measured between:

A. Mirror and reflected ray

B. Normal and reflected ray

C. Incident ray and mirror

D. Incident ray and reflected ray

Answer: B

Q3. According to the second law of reflection:

A. i > r

B. i < r

C. i = r

D. i + r = 180°

Answer: C

Q4. The incident ray, reflected ray and normal lie:

A. In different planes

B. In perpendicular planes

C. In parallel planes

D. In the same plane

Answer: D

Q5. A plane mirror forms an image that is:

A. Virtual and erect

B. Real and erect

C. Real and inverted

D. Virtual and inverted

Answer: A

Q6. The image formed by a plane mirror is:

A. Larger

B. Same size

C. Smaller

D. Sometimes zero

Answer: B

Q7. The reversal of left and right in a plane mirror is called:

A. Dispersion

B. Refraction

C. Lateral inversion

D. Diffraction

Answer: C

Q8. Which surface gives regular reflection?

A. Rough wall

B. Paper

C. Cloth

D. Polished mirror

Answer: D

Q9. Diffuse reflection occurs mainly from:

A. Rough surfaces

B. Perfectly smooth surfaces

C. Plane mirrors only

D. Vacuum

Answer: A

Q10. A concave mirror is also called a:

A. Diverging mirror

B. Converging mirror

C. Plane mirror

D. Transparent mirror

Answer: B

Q11. A convex mirror is:

A. Converging

B. Plane

C. Diverging

D. Absorbing

Answer: C

Q12. The centre of the sphere of which a spherical mirror forms a part is called:

A. Pole

B. Focus

C. Aperture

D. Centre of curvature

Answer: D

Q13. The relation between radius of curvature and focal length is:

A. R = 2f

B. R = f/2

C. R = f²

D. R = 4f

Answer: A

Q14. The mirror formula is:

A. 1/f = 1/u − 1/v

B. 1/f = 1/v + 1/u

C. f = u + v

D. f = uv

Answer: B

Q15. Magnification of a spherical mirror is:

A. v/u

B. u/v

C. −v/u

D. uv

Answer: C

Q16. If magnification is negative, the image is:

A. Virtual

B. Erect

C. Same size

D. Inverted

Answer: D

Q17. A convex mirror always forms an image that is:

A. Virtual, erect and diminished

B. Real and enlarged

C. Real and inverted

D. Real and same size

Answer: A

Q18. When an object is placed at C of a concave mirror, the image is:

A. At F and enlarged

B. At C and same size

C. Behind mirror and enlarged

D. At P and diminished

Answer: B

Q19. When an object is placed between F and P of a concave mirror, the image is:

A. Real and diminished

B. Real and same size

C. Virtual, erect and magnified

D. Real and inverted

Answer: C

Q20. A convex mirror is used as a rear-view mirror because:

A. It forms real images

B. It magnifies everything

C. It forms inverted images

D. It gives a wider field of view

Answer: D

Q21. A ray passing through the centre of curvature of a concave mirror:

A. Retraces its path

B. Passes through F

C. Becomes parallel

D. Is absorbed

Answer: A

Q22. A ray parallel to the principal axis of a concave mirror is reflected:

A. Through P

B. Through F

C. Through C only

D. Behind the mirror only

Answer: B

Q23. If the focal length of a concave mirror is 10 cm, its radius of curvature is:

A. 5 cm

B. 10 cm

C. 20 cm

D. 40 cm

Answer: C

R = 2f = 2 × 10 = 20 cm.

Q24. If two plane mirrors are placed at 90°, the number of images is:

A. 1

B. 2

C. 4

D. 3

Answer: D

n = 360/90 − 1 = 3.

Q25. The pole of a spherical mirror is represented by:

A. P

B. F

C. C

D. R

Answer: A

Q26. The principal axis passes through:

A. F only

B. P and C

C. F only and not P

D. Mirror edge only

Answer: B

Q27. If m = +2 for a spherical mirror, the image is:

A. Inverted and diminished

B. Inverted and magnified

C. Erect and magnified

D. Erect and diminished

Answer: C

Q28. A concave mirror can produce:

A. Only virtual images

B. Only diminished images

C. Only erect images

D. Real as well as virtual images

Answer: D

Q29. The image formed by a plane mirror is laterally inverted but:

A. Has the same size as the object

B. Is always enlarged

C. Is always diminished

D. Is always real

Answer: A

Q30. A concave mirror is useful as a shaving mirror because:

A. It always gives a diminished image

B. It can produce an enlarged erect image when the object is within F

C. It gives a wide field of view

D. It does not reflect light

Answer: B

24. 30 Subjective Questions with Answers

2 Marks Q1. Define reflection of light.

प्रकाश के किसी सतह से टकराकर उसी माध्यम में वापस लौटने की घटना को प्रकाश का परावर्तन कहते हैं।

2 Marks Q2. What is an incident ray?

The ray of light falling on the reflecting surface is called the incident ray.

2 Marks Q3. State the two laws of reflection.

1. Incident ray, reflected ray and normal lie in the same plane.
2. Angle of incidence equals angle of reflection.

2 Marks Q4. What is lateral inversion?

The sideways reversal of an object in a plane mirror is called lateral inversion.

2 Marks Q5. Give two properties of the image formed by a plane mirror.

The image is virtual and erect. It is also of the same size as the object.

3 Marks Q6. Differentiate between regular and diffuse reflection.

Regular reflection occurs on smooth surfaces and gives parallel reflected rays. Diffuse reflection occurs on rough surfaces and the reflected rays scatter in different directions.

3 Marks Q7. Explain why a plane mirror forms a virtual image.

Reflected rays actually travel in front of the mirror but appear to come from behind it when extended backward. Therefore, the image is virtual and cannot be obtained on a screen.

3 Marks Q8. Define pole, centre of curvature and focal length.

Pole is the centre of the reflecting surface. Centre of curvature is the centre of the sphere of which the mirror is a part. Focal length is the distance between pole and principal focus.

3 Marks Q9. Why is a convex mirror used as a rear-view mirror?

It forms an erect and diminished image and provides a wider field of view, allowing the driver to see a larger area behind the vehicle.

3 Marks Q10. State the relation between radius of curvature and focal length.

For a spherical mirror:
R = 2f
Thus focal length is approximately half the radius of curvature.

4 Marks Q11. Explain the image formed by a concave mirror when the object is at C.

When the object is placed at C:

• Image is formed at C.
• Image is real.
• Image is inverted.
• Image is of the same size as the object.

4 Marks Q12. Explain the image formed by a convex mirror.

A convex mirror forms a virtual, erect and diminished image behind the mirror between P and F for a real object placed anywhere in front of it.

4 Marks Q13. Explain the significance of the normal in reflection.

The normal is an imaginary line perpendicular to the reflecting surface at the point of incidence. Angles of incidence and reflection are measured from the normal. The law of reflection is expressed as ∠i = ∠r.

4 Marks Q14. Write four properties of the image formed by a plane mirror.

The image is:

1. Virtual
2. Erect
3. Same size as object
4. Laterally inverted

4 Marks Q15. Explain multiple reflection with two examples.

Repeated reflection of light from more than one reflecting surface is called multiple reflection. Examples include a periscope and kaleidoscope.

5 Marks Q16. Derive the mirror formula.

For a spherical mirror under the paraxial approximation, applying the geometry of ray reflection leads to the mirror relation:

1/f = 1/v + 1/u

Here u is object distance, v is image distance and f is focal length, measured according to the New Cartesian Sign Convention.

5 Marks Q17. Explain the New Cartesian Sign Convention for spherical mirrors.

• Pole is taken as origin.
• Principal axis is the reference axis.
• Distances measured in the direction of incident light are positive.
• Distances measured opposite to incident light are negative.
• Heights above principal axis are positive.
• Heights below principal axis are negative.

5 Marks Q18. Explain the important rays used in concave mirror ray diagrams.

• Parallel ray → reflected through F.
• Ray through F → reflected parallel to principal axis.
• Ray through C → retraces its path.

5 Marks Q19. Differentiate between concave and convex mirrors.

Concave mirror is converging and can form real or virtual images. Convex mirror is diverging and normally forms virtual, erect and diminished images for real objects. Concave mirrors are used in headlights and shaving mirrors; convex mirrors are used as rear-view mirrors.

5 Marks Q20. Explain why diffuse reflection does not violate the laws of reflection.

A rough surface has many differently oriented small surface elements. Each incident ray obeys ∠i = ∠r with respect to the local normal. Since the normals differ from point to point, reflected rays travel in different directions. Hence diffuse reflection still follows the laws of reflection.

6 Marks Q21. Explain all possible image positions for a concave mirror.

Object	Image	Nature
Beyond C	Between F and C	Real, inverted, diminished
At C	At C	Real, inverted, same size
Between C and F	Beyond C	Real, inverted, magnified
At F	At infinity	Highly enlarged
Between F and P	Behind mirror	Virtual, erect, magnified

6 Marks Q22. Explain the working principle and applications of a concave mirror.

A concave mirror converges parallel rays toward its principal focus. This property is used in vehicle headlights, searchlights, solar furnaces, reflecting telescopes and shaving mirrors. The exact image nature depends on the position of the object.

6 Marks Q23. Explain the working principle and applications of a convex mirror.

A convex mirror diverges reflected rays. The rays appear to come from a focus behind the mirror. It always forms a virtual, erect and diminished image for a real object. Therefore it is useful in vehicle rear-view mirrors, security mirrors and road-corner mirrors.

6 Marks Q24. Explain mirror formula and magnification with sign convention.

Mirror formula:

1/f = 1/v + 1/u

Magnification:

m = hᵢ/hₒ = −v/u

The signs of u, v, f and heights are assigned using the New Cartesian Sign Convention.

6 Marks Q25. Explain reflection of light with a labelled diagram.

A light ray falling on a reflecting surface is incident ray. The ray returning from the surface is reflected ray. A perpendicular drawn at the point of incidence is normal. The angle between incident ray and normal is i and between reflected ray and normal is r. According to the law of reflection, i = r.

6 Marks Q26. Why can we see non-luminous objects?

Non-luminous objects do not produce their own light. Light from a luminous source falls on them and gets reflected. Some of the reflected light enters our eyes, allowing us to see the objects.

6 Marks Q27. Explain regular reflection and diffuse reflection with examples.

Regular reflection occurs on smooth surfaces and reflected rays remain orderly, producing clear images. Diffuse reflection occurs on rough surfaces and reflected rays spread in different directions. Both obey the laws of reflection individually.

6 Marks Q28. Explain why the image in a plane mirror cannot be obtained on a screen.

The rays reflected from a plane mirror do not actually meet behind the mirror. Their backward extensions only appear to meet at the image position. Hence the image is virtual and cannot be captured on a screen.

6 Marks Q29. Explain the applications of different mirrors.

• Plane mirror: dressing mirrors and periscopes.
• Concave mirror: headlights, solar furnace, shaving mirror, searchlight.
• Convex mirror: rear-view and security mirrors.

6 Marks Q30. Explain why a concave mirror is called a converging mirror and a convex mirror a diverging mirror.

A concave mirror reflects parallel rays toward a common region near its principal focus, so it is called a converging mirror. A convex mirror reflects parallel rays outward so that they appear to diverge from a focus behind the mirror; therefore it is called a diverging mirror.

25. Assertion–Reason Questions

Q1. Assertion: The angle of incidence is equal to the angle of reflection.
Reason: Both angles are measured from the normal.

Answer: Both Assertion and Reason are true, and Reason correctly explains the measurement basis, though the equality itself follows from the law of reflection.

Q2. Assertion: A convex mirror is used as a rear-view mirror.
Reason: It provides a wider field of view.

Answer: Both are true and Reason correctly explains the Assertion.

Q3. Assertion: A plane mirror forms a virtual image.
Reason: Reflected rays actually meet behind the mirror.

Answer: Assertion is true but Reason is false. The rays only appear to meet behind the mirror.

Q4. Assertion: A concave mirror can form a real image.
Reason: A concave mirror can converge reflected rays.

Answer: Both are true and Reason correctly explains the Assertion.

Q5. Assertion: Diffuse reflection violates the law of reflection.
Reason: Reflected rays travel in different directions from a rough surface.

Answer: Assertion is false but Reason is true. Every individual ray still obeys the law of reflection.

26. HOTS | Higher Order Thinking Questions

HOTS 1: Why is a convex mirror preferred over a plane mirror for vehicle rear-view mirrors?

A convex mirror provides a wider field of view and forms an erect, diminished image, allowing the driver to observe a larger region behind the vehicle.

HOTS 2: Why does a concave mirror work as a shaving mirror?

When the face is placed between the pole and focus, the concave mirror forms a virtual, erect and magnified image.

HOTS 3: A student says diffuse reflection means no reflection occurs. Is the statement correct?

No. Reflection occurs, but rough surfaces cause reflected rays to travel in different directions because their local normals are differently oriented.

HOTS 4: Why does a ray passing through C of a concave mirror return along the same path?

The ray strikes the spherical surface normally because it is directed along the radius through C. Therefore i = 0° and r = 0°, so it retraces its path.

HOTS 5: Can a concave mirror produce both real and virtual images? Explain.

Yes. When the object is outside F, the image is generally real and inverted. When the object lies between F and P, the image becomes virtual, erect and magnified.

27. Important Numericals

Numerical 1: A concave mirror has focal length 15 cm. Find its radius of curvature.

R = 2f
R = 2 × 15
R = 30 cm

Numerical 2: An object is placed 20 cm in front of a concave mirror of focal length 10 cm. Find the image distance.

Using New Cartesian Sign Convention:
u = −20 cm
f = −10 cm

1/f = 1/v + 1/u
−1/10 = 1/v − 1/20
1/v = −1/20
v = −20 cm

The image is formed 20 cm in front of the mirror.

Numerical 3: An object of height 5 cm is placed before a mirror and forms an image of height −10 cm. Find magnification.

m = hᵢ/hₒ
m = −10/5
m = −2

Negative sign indicates an inverted image and magnitude 2 indicates the image is twice the object size.

Numerical 4: Two plane mirrors are placed at an angle of 60°. Find the number of images in the usual symmetric arrangement.

n = 360/θ − 1
n = 360/60 − 1
n = 6 − 1
n = 5 images

Numerical 5: A spherical mirror has radius of curvature 40 cm. Find its focal length.

R = 2f
40 = 2f
f = 20 cm

28. Diagram Labelling Practice

Labels to remember: P = Pole, F = Principal Focus, C = Centre of Curvature, R = Radius of Curvature, f = Focal Length.

29. CBSE Golden Points ⭐

• Reflection means return of light into the same medium.
• ∠i = ∠r.
• Angles are measured from the normal.
• Plane mirror image is virtual, erect and same size.
• Plane mirror produces lateral inversion.
• Concave mirror is converging.
• Convex mirror is diverging.
• R = 2f.
• Mirror formula: 1/f = 1/v + 1/u.
• Magnification: m = −v/u.
• Convex mirror gives a wider field of view.
• Concave mirror can form real as well as virtual images.
• A ray through C retraces its path.
• A parallel ray to a concave mirror is reflected through F.
• Diffuse reflection still obeys the laws of reflection.

30. Memory Tricks 🧠

Reflection Laws:
“Same Plane + Same Angle”

Same Plane → Incident ray + Reflected ray + Normal
Same Angle → i = r

Mirror Types:
Concave = Converging
Convex = Diverging

Formula Trick:
“R is Twice f”
R = 2f

Plane Mirror:
V-E-S-L
Virtual – Erect – Same size – Laterally inverted

31. One-Line Revision

Light + Reflecting Surface → Reflection → ∠i = ∠r

Concave → Converging | Convex → Diverging

Plane Mirror → Virtual + Erect + Same Size + Laterally Inverted

32. Final Summary | अंतिम सारांश

Reflection of Light is the phenomenon in which light returns into the same medium after striking a reflecting surface.

The two laws of reflection are fundamental:
1. Incident ray, reflected ray and normal lie in the same plane.
2. Angle of incidence equals angle of reflection.

Plane mirrors produce virtual, erect, same-sized and laterally inverted images.

Spherical mirrors are of two types:
Concave mirror → Converging
Convex mirror → Diverging

Important formulas:

∠i = ∠r

R = 2f

1/f = 1/v + 1/u

m = −v/u

🔦 Light – Reflection and Refraction

Reflection of Light | Class 10 Science | CBSE + Foundation + Competitive

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