🔦 Light – Reflection and Refraction | Laws of Reflection
Class 10 Science | CBSE + Foundation + Competitive Level
📐 Laws of Reflection | परावर्तन के नियम
1. Introduction to Laws of Reflection | परावर्तन के नियमों का परिचय
Reflection of Light:
जब प्रकाश किसी परावर्तक सतह से टकराकर उसी माध्यम में वापस लौटता है, तो इस घटना को प्रकाश का परावर्तन कहते हैं।
When light strikes a reflecting surface and returns into the same medium, the phenomenon is called reflection of light.
Reflection follows two fundamental laws known as the Laws of Reflection.
When light strikes a reflecting surface and returns into the same medium, the phenomenon is called reflection of light.
Reflection follows two fundamental laws known as the Laws of Reflection.
Incident Ray
Point of Incidence
Normal
Reflected Ray
2. Important Terms | महत्वपूर्ण शब्दावली
| Term | Meaning | Hindi |
|---|---|---|
| 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 | Line perpendicular to reflecting surface 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. What is Normal? | अभिलम्ब क्या है?
Normal:
The normal is an imaginary line drawn perpendicular to the reflecting surface at the point of incidence.
आपतन बिंदु पर परावर्तक सतह के लंबवत खींची गई काल्पनिक रेखा को अभिलम्ब (Normal) कहते हैं।
आपतन बिंदु पर परावर्तक सतह के लंबवत खींची गई काल्पनिक रेखा को अभिलम्ब (Normal) कहते हैं।
Very Important:
Angle of incidence and angle of reflection are measured from the normal, not from the mirror surface.
आपतन कोण और परावर्तन कोण हमेशा Normal से मापे जाते हैं।
आपतन कोण और परावर्तन कोण हमेशा Normal से मापे जाते हैं।
4. Animated Diagram – Laws of Reflection
5. First Law of Reflection | परावर्तन का प्रथम नियम
Statement:
The incident ray, reflected ray and the normal at the point of incidence all lie in the same plane.
हिंदी: आपतित किरण, परावर्तित किरण तथा आपतन बिंदु पर खींचा गया अभिलम्ब तीनों एक ही तल में होते हैं।
हिंदी: आपतित किरण, परावर्तित किरण तथा आपतन बिंदु पर खींचा गया अभिलम्ब तीनों एक ही तल में होते हैं।
First Law Memory Trick:
👉 Incident + Reflected + Normal = Same Plane
आपतित किरण + परावर्तित किरण + अभिलम्ब = एक ही तल
👉 Incident + Reflected + Normal = Same Plane
आपतित किरण + परावर्तित किरण + अभिलम्ब = एक ही तल
6. Second Law of Reflection | परावर्तन का द्वितीय नियम
Statement:
The angle of incidence is equal to the angle of reflection.
हिंदी: आपतन कोण परावर्तन कोण के बराबर होता है।
हिंदी: आपतन कोण परावर्तन कोण के बराबर होता है।
∠i = ∠r
Example:
If angle of incidence = 40°,
then angle of reflection = 40°.
7. Angle of Incidence | आपतन कोण
The angle between the incident ray and the normal at the point of incidence is called the angle of incidence.
आपतित किरण तथा अभिलम्ब के बीच बने कोण को आपतन कोण (i) कहते हैं।
आपतित किरण तथा अभिलम्ब के बीच बने कोण को आपतन कोण (i) कहते हैं।
i = Angle between Incident Ray and Normal
8. Angle of Reflection | परावर्तन कोण
The angle between the reflected ray and the normal is called the angle of reflection.
परावर्तित किरण तथा अभिलम्ब के बीच बने कोण को परावर्तन कोण (r) कहते हैं।
परावर्तित किरण तथा अभिलम्ब के बीच बने कोण को परावर्तन कोण (r) कहते हैं।
r = Angle between Reflected Ray and Normal
9. Relation Between i and r
i = r
| Angle of Incidence | Angle of Reflection |
|---|---|
| 20° | 20° |
| 30° | 30° |
| 45° | 45° |
| 60° | 60° |
| 90° | 90° |
10. Special Case: Normal Incidence
When a light ray falls normally on a reflecting surface, the angle of incidence is:
i = 0°
According to the law of reflection:
r = 0°
Therefore, the ray retraces its path.
अर्थात प्रकाश की किरण उसी मार्ग से वापस लौटती है।
अर्थात प्रकाश की किरण उसी मार्ग से वापस लौटती है।
11. If Angle with Mirror Surface is Given
Sometimes a question gives the angle made by the incident ray with the mirror surface instead of the normal.
Since normal is perpendicular to the mirror:
Angle with Normal = 90° − Angle with Mirror
Example:
If the incident ray makes 30° with the mirror surface:
i = 90° − 30°
i = 60°
Therefore, r = 60°.
i = 90° − 30°
i = 60°
Therefore, r = 60°.
12. Experimental Verification of Laws of Reflection
The laws of reflection can be experimentally verified using:
- Plane mirror
- Drawing board
- White paper
- Optical pins
- Protractor
- Pencil
13. Experiment – Verification of Second Law
Procedure:
- Fix a plane mirror vertically on a sheet of paper.
- Draw a normal at the point of incidence.
- Draw an incident ray making a known angle with the normal.
- Observe the reflected ray using optical pins.
- Measure the angle of incidence and angle of reflection.
- Repeat the experiment for different angles.
| Trial | i | r |
|---|---|---|
| 1 | 20° | 20° |
| 2 | 30° | 30° |
| 3 | 40° | 40° |
| 4 | 50° | 50° |
Conclusion:
The angle of incidence is equal to the angle of reflection.
14. Experimental Verification of First Law
The incident ray, reflected ray and normal are observed to lie in the same plane.
इस प्रकार प्रयोग द्वारा यह सत्यापित किया जा सकता है कि आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में स्थित होते हैं।
इस प्रकार प्रयोग द्वारा यह सत्यापित किया जा सकता है कि आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में स्थित होते हैं।
15. Important Experimental Precautions
- Mirror should be placed vertically.
- Pins should be fixed vertically.
- Distances between pins should be sufficiently large.
- Eye should be kept at the same level as the pins.
- Parallax error should be avoided.
- Angles should be measured from the normal.
- The reflecting surface should be properly aligned.
16. Reflection from a Plane Mirror
A plane mirror produces a virtual image behind the mirror.
Important properties:
| Property | Image |
|---|---|
| Nature | Virtual |
| Orientation | Erect |
| Size | Same as object |
| Position | Same distance behind mirror as object is in front |
| Lateral Inversion | Present |
17. Regular Reflection
Regular reflection occurs when parallel incident rays fall on a smooth reflecting surface and remain orderly after reflection.
Examples:
Examples:
- Plane mirror
- Polished metal
- Still water surface
18. Diffuse Reflection
Diffuse reflection occurs from a rough surface.
The reflected rays travel in different directions because the surface normals are differently oriented.
Important CBSE Point:
Diffuse reflection does not violate the laws of reflection.
हर individual ray अपने local normal के अनुसार i = r का पालन करती है।
19. Regular vs Diffuse Reflection
| Regular Reflection | Diffuse Reflection |
|---|---|
| Smooth surface | Rough surface |
| Reflected rays remain orderly | Reflected rays scatter |
| Clear image can form | Clear image generally does not form |
| Example: Mirror | Example: Wall |
20. Why Do We See Objects?
We see an object when light from a source reaches the object and reflected light enters our eyes.
हम किसी वस्तु को तब देखते हैं जब प्रकाश उस वस्तु से परावर्तित होकर हमारी आँखों में प्रवेश करता है।
हम किसी वस्तु को तब देखते हैं जब प्रकाश उस वस्तु से परावर्तित होकर हमारी आँखों में प्रवेश करता है।
Light Source
→
Object
→
Reflected Light
→
Eye
21. Important Applications of Reflection
| Application | Principle |
|---|---|
| Plane mirror | Regular reflection |
| Rear-view mirror | Convex mirror |
| Shaving mirror | Concave mirror |
| Headlight reflector | Reflection by concave reflector |
| Periscope | Multiple reflection |
| Kaleidoscope | Multiple reflection |
22. Common Mistakes in Laws of Reflection
Mistake 1:
Angle is measured from mirror.
❌ Wrong
Correct: Angle is measured from the normal.
Mistake 2: i ≠ r
❌ Wrong
Correct: i = r
Mistake 3: Diffuse reflection violates reflection law.
❌ Wrong
Correct: Each ray still obeys i = r.
❌ Wrong
Correct: Angle is measured from the normal.
Mistake 2: i ≠ r
❌ Wrong
Correct: i = r
Mistake 3: Diffuse reflection violates reflection law.
❌ Wrong
Correct: Each ray still obeys i = r.
23. 30 MCQs | Multiple Choice Questions
Q1. The angle of incidence is measured between:
A. Incident ray and normal
B. Incident ray and mirror
C. Reflected ray and mirror
D. Incident and reflected rays
Answer: A
Q2. The angle of reflection is measured between:
A. Reflected ray and mirror
B. Reflected ray and normal
C. Incident ray and mirror
D. Incident ray and normal
Answer: B
Q3. According to the second law of reflection:
A. i > r
B. i < r
C. i = r
D. i + r = 90°
Answer: C
Q4. The incident ray, reflected ray and normal lie:
A. In different planes
B. In parallel planes
C. At right angles always
D. In the same plane
Answer: D
Q5. If i = 30°, then r is:
A. 30°
B. 60°
C. 90°
D. 15°
Answer: A
Q6. If angle of incidence is 45°, angle of reflection is:
A. 90°
B. 45°
C. 30°
D. 15°
Answer: B
Q7. The perpendicular drawn at the point of incidence is called:
A. Incident ray
B. Reflected ray
C. Normal
D. Mirror axis
Answer: C
Q8. If a ray falls normally on a mirror, the angle of incidence is:
A. 90°
B. 45°
C. 180°
D. 0°
Answer: D
Q9. For normal incidence, the reflected ray:
A. Retraces its path
B. Bends toward the surface
C. Becomes parallel to mirror
D. Is absorbed
Answer: A
Q10. The first law of reflection deals with:
A. Speed of light
B. Same plane of rays and normal
C. Refractive index
D. Magnification
Answer: B
Q11. The second law of reflection gives the relation:
A. i + r = 90°
B. i − r = 90°
C. i = r
D. i = 2r
Answer: C
Q12. Reflection takes place when light:
A. Enters another medium
B. Is absorbed completely
C. Splits into colours
D. Returns into the same medium
Answer: D
Q13. If a ray makes 20° with the mirror surface, its angle of incidence is:
A. 70°
B. 20°
C. 90°
D. 40°
Answer: A
i = 90° − 20° = 70°.
Q14. If i = 70°, r equals:
A. 20°
B. 70°
C. 35°
D. 90°
Answer: B
Q15. Which law states that the three rays/lines lie in the same plane?
A. Second law
B. Law of refraction
C. First law
D. Snell's law
Answer: C
Q16. Which surface generally produces regular reflection?
A. Rough wall
B. Cloth
C. Paper
D. Polished mirror
Answer: D
Q17. Diffuse reflection occurs mainly on:
A. Rough surfaces
B. Perfectly polished mirrors
C. Plane glass only
D. Vacuum
Answer: A
Q18. Diffuse reflection:
A. Violates reflection law
B. Still obeys reflection law for each ray
C. Is not reflection
D. Occurs only in darkness
Answer: B
Q19. If the incident ray and reflected ray make 80° with each other, i is:
A. 20°
B. 80°
C. 40°
D. 10°
Answer: C
Angle between incident and reflected rays = 2i. Therefore 2i = 80°, so i = 40°.
Q20. If i = 0°, the angle between incident and reflected rays is:
A. 90°
B. 180°
C. 45°
D. 0°
Answer: D
Q21. A normal is drawn at:
A. Point of incidence
B. End of mirror
C. Centre of mirror always
D. Any random point
Answer: A
Q22. If a ray makes 60° with the mirror surface, angle of incidence is:
A. 60°
B. 30°
C. 120°
D. 90°
Answer: B
Q23. If i = 35°, then r =:
A. 55°
B. 70°
C. 35°
D. 145°
Answer: C
Q24. The laws of reflection are applicable to:
A. Regular reflection only
B. Plane mirrors only
C. Concave mirrors only
D. Reflection in general
Answer: D
Q25. The angle between the mirror and its normal is:
A. 90°
B. 0°
C. 45°
D. 180°
Answer: A
Q26. A plane mirror reflects light according to:
A. Law of conservation of mass
B. Laws of reflection
C. Law of gravitation
D. Ohm's law
Answer: B
Q27. If angle with the normal is 25°, angle with the mirror surface is:
A. 25°
B. 90°
C. 65°
D. 50°
Answer: C
Q28. Which of the following is NOT a part of the first law?
A. Incident ray
B. Reflected ray
C. Normal
D. Refractive index
Answer: D
Q29. The equality i = r is known as:
A. Second law of reflection
B. First law of reflection
C. Law of refraction
D. Snell's law
Answer: A
Q30. A ray incident normally on a plane mirror is reflected:
A. At 45°
B. Back along the same path
C. Parallel to the mirror
D. At 90° to normal
Answer: B
24. 30 Subjective Questions with Answers
2 Marks
Q1. State the first law of reflection.
The incident ray, reflected ray and normal at the point of incidence lie in the same plane.
आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में होते हैं।
आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में होते हैं।
2 Marks
Q2. State the second law of reflection.
The angle of incidence is equal to the angle of reflection.
i = r
i = r
2 Marks
Q3. Define angle of incidence.
The angle between the incident ray and normal at the point of incidence is called the angle of incidence.
2 Marks
Q4. Define angle of reflection.
The angle between the reflected ray and normal at the point of incidence is called the angle of reflection.
2 Marks
Q5. What is a normal?
A perpendicular line drawn to the reflecting surface at the point of incidence is called the normal.
3 Marks
Q6. Why are angles of reflection measured from the normal?
The laws of reflection define the angle with respect to the normal. The normal is perpendicular to the surface and provides a fixed reference for measuring the incident and reflected directions.
3 Marks
Q7. What happens when light falls normally on a mirror?
For normal incidence, i = 0°. Therefore r = 0°. The reflected ray retraces the path of the incident ray.
3 Marks
Q8. If i = 40°, find r.
According to the second law:
i = r
Therefore,
r = 40°
i = r
Therefore,
r = 40°
3 Marks
Q9. What is the difference between angle with mirror and angle with normal?
The mirror and normal are perpendicular. Therefore:
Angle with normal = 90° − angle with mirror.
Angle with normal = 90° − angle with mirror.
3 Marks
Q10. What is diffuse reflection?
Diffuse reflection is reflection from a rough surface in which reflected rays travel in different directions. Each individual ray still obeys the law of reflection.
4 Marks
Q11. Explain both laws of reflection.
First Law: Incident ray, reflected ray and normal lie in the same plane.
Second Law: Angle of incidence equals angle of reflection.
i = r
Second Law: Angle of incidence equals angle of reflection.
i = r
4 Marks
Q12. Explain the terms incident ray, reflected ray and normal.
Incident ray falls on the reflecting surface. Reflected ray returns from the surface. Normal is the perpendicular line drawn at the point of incidence.
4 Marks
Q13. Differentiate between regular and diffuse reflection.
Regular reflection occurs on smooth surfaces and reflected rays remain orderly.
Diffuse reflection occurs on rough surfaces and reflected rays scatter in different directions.
Diffuse reflection occurs on rough surfaces and reflected rays scatter in different directions.
4 Marks
Q14. Why does diffuse reflection not violate the laws of reflection?
Every individual ray obeys i = r with respect to the normal at its point of incidence. Different orientations of surface elements cause the reflected rays to travel in different directions.
4 Marks
Q15. Explain normal incidence.
When an incident ray falls perpendicular to the reflecting surface, it is called normal incidence. The angle of incidence is 0° and angle of reflection is also 0°. Therefore, the ray retraces its path.
5 Marks
Q16. Describe an experiment to verify the second law of reflection.
- Place a plane mirror vertically on a drawing sheet.
- Draw a normal at the point of incidence.
- Draw an incident ray at a known angle.
- Use optical pins to locate the reflected ray.
- Measure i and r using a protractor.
- Repeat for different angles.
- Observe that i = r.
5 Marks
Q17. Explain the experiment for verifying the first law of reflection.
A plane mirror is placed on a sheet and an incident ray is drawn. The reflected ray is located using pins. A normal is drawn at the point of incidence. The incident ray, reflected ray and normal are found to lie in the same plane. Hence the first law is verified.
5 Marks
Q18. Explain why the angle between the incident ray and reflected ray is 2i.
Let the angle of incidence be i.
According to the law of reflection:
r = i
The normal lies between the incident and reflected rays. Therefore:
Angle between incident and reflected rays
= i + r
= i + i
= 2i
r = i
The normal lies between the incident and reflected rays. Therefore:
Angle between incident and reflected rays
= i + r
= i + i
= 2i
5 Marks
Q19. Explain the importance of the normal in reflection.
The normal provides the reference line for measuring the angles of incidence and reflection. It is perpendicular to the reflecting surface at the point of incidence and helps us apply the relation i = r correctly.
5 Marks
Q20. Explain reflection of light using a labelled ray diagram.
A ray falling on the surface is incident ray. At the point of incidence a normal is drawn perpendicular to the surface. The returning ray is reflected ray. The angle between incident ray and normal is i and between reflected ray and normal is r. According to the second law, i = r.
6 Marks
Q21. Explain the two laws of reflection with suitable examples.
First Law:
The incident ray, reflected ray and normal lie in the same plane.
Example: In a plane mirror experiment, all three can be represented on the same sheet of paper.
Second Law: The angle of incidence equals the angle of reflection.
i = r
Example: If i = 45°, then r = 45°.
Example: In a plane mirror experiment, all three can be represented on the same sheet of paper.
Second Law: The angle of incidence equals the angle of reflection.
i = r
Example: If i = 45°, then r = 45°.
6 Marks
Q22. Describe a complete experiment to verify the laws of reflection.
Apparatus:
Plane mirror, drawing board, paper, optical pins, scale and protractor.
Procedure:
Conclusion: Both laws of reflection are verified.
Procedure:
- Fix the mirror vertically.
- Mark the point of incidence.
- Draw a normal.
- Draw an incident ray at a selected angle.
- Locate the reflected ray using pins.
- Measure i and r.
- Repeat the experiment.
Conclusion: Both laws of reflection are verified.
6 Marks
Q23. Explain why the angle made by the incident ray with the mirror is not the angle of incidence.
The angle of incidence is defined between the incident ray and the normal, not the mirror surface. Since normal is perpendicular to the mirror, if a ray makes θ with the mirror, its angle of incidence is 90° − θ.
6 Marks
Q24. Explain regular and diffuse reflection and their relation with the laws of reflection.
Regular reflection occurs from smooth surfaces and gives an orderly reflected beam. Diffuse reflection occurs from rough surfaces and the reflected rays spread in different directions. In both cases, each ray follows the laws of reflection. Diffuse reflection is caused by different orientations of surface normals.
6 Marks
Q25. Explain the significance of i = r in ray diagrams.
The relation i = r allows us to determine the exact direction of the reflected ray when the incident ray and normal are known. It is fundamental for drawing ray diagrams and solving numerical problems based on reflection.
6 Marks
Q26. What happens to the reflected ray when the angle of incidence is gradually increased?
As the angle of incidence increases, the angle of reflection increases by the same amount because i = r. Thus the reflected ray changes its direction symmetrically with respect to the normal.
6 Marks
Q27. Explain the role of optical pins in verification of reflection laws.
Optical pins help locate the path of the incident and reflected rays. By aligning the images of pins and observing them from a suitable position, the direction of the reflected ray can be determined. Measuring the resulting angles verifies the laws of reflection.
6 Marks
Q28. Write important precautions for the reflection experiment.
- Mirror should be vertical.
- Pins should be vertical.
- Parallax error should be avoided.
- Eye should be at suitable level.
- Mirror should be properly aligned.
- Angles must be measured from the normal.
6 Marks
Q29. A ray makes 35° with the mirror surface. Find i and r.
Angle with mirror = 35°
Angle with normal:
i = 90° − 35°
i = 55°
According to reflection law:
r = i
r = 55°
Angle with normal:
i = 90° − 35°
i = 55°
According to reflection law:
r = i
r = 55°
6 Marks
Q30. Explain the complete path of light during reflection.
Light travels toward a reflecting surface as the incident ray. At the point of incidence, a normal is drawn. The light returns into the same medium as the reflected ray. The incident ray, reflected ray and normal lie in the same plane, and the angles satisfy:
i = r
Thus the direction of reflected light is completely determined by the laws of reflection.
25. Assertion–Reason Questions
Q1.
Assertion: The angle of incidence is equal to the angle of reflection.
Reason: This is the second law of reflection.
Reason: This is the second law of reflection.
Answer: Both Assertion and Reason are true, and Reason correctly identifies the law.
Q2.
Assertion: Angles of incidence and reflection are measured from the normal.
Reason: The normal is perpendicular to the reflecting surface.
Reason: The normal is perpendicular to the reflecting surface.
Answer: Both statements are true, but the Reason describes the nature of the normal rather than directly stating why the law defines the angles that way.
Q3.
Assertion: Diffuse reflection violates the laws of reflection.
Reason: Reflected rays from a rough surface travel in different directions.
Reason: Reflected rays from a rough surface travel in different directions.
Answer: Assertion is false, but Reason is true.
Q4.
Assertion: If i = 40°, then r = 40°.
Reason: Angle of incidence is equal to angle of reflection.
Reason: Angle of incidence is equal to angle of reflection.
Answer: Both are true and Reason correctly explains the Assertion.
Q5.
Assertion: A ray incident normally on a plane mirror retraces its path.
Reason: For normal incidence, i = r = 0°.
Reason: For normal incidence, i = r = 0°.
Answer: Both are true and Reason correctly explains the Assertion.
26. HOTS | Higher Order Thinking Questions
HOTS 1:
A student measures the angle of incidence from the mirror surface instead of the normal. Will the result be correct?
No. The angle of incidence must be measured from the normal. If the ray makes θ with the mirror surface, the actual incidence angle is 90° − θ.
HOTS 2:
Why does a ray falling normally on a mirror return along the same path?
At normal incidence, i = 0°. By the second law r = 0°. Hence the reflected ray travels back along the incident path.
HOTS 3:
If the angle of incidence is increased by 10°, by how much will the angle of reflection change?
It will also increase by 10° because i = r.
HOTS 4:
Why can a rough wall be seen from many directions even though it does not form a clear image?
The rough surface produces diffuse reflection. Different surface elements reflect light in different directions, allowing light to reach observers from many directions.
HOTS 5:
If the angle between incident and reflected rays is 120°, find the angle of incidence.
Angle between incident and reflected rays = 2i.
2i = 120°
i = 60°
2i = 120°
i = 60°
27. Important Numericals
Numerical 1:
A ray falls on a plane mirror at an angle of incidence 35°. Find the angle of reflection.
By law of reflection:
i = r
r = 35°
Answer: 35°
i = r
r = 35°
Answer: 35°
Numerical 2:
A ray makes an angle of 25° with the mirror surface. Find the angle of incidence and reflection.
i = 90° − 25°
i = 65°
r = i
r = 65°
i = 65°
r = i
r = 65°
Numerical 3:
The angle between the incident and reflected rays is 100°. Find i and r.
Angle between incident and reflected rays = 2i
2i = 100°
i = 50°
r = 50°
Answer: i = 50°, r = 50°
2i = 100°
i = 50°
r = 50°
Answer: i = 50°, r = 50°
Numerical 4:
If the angle of reflection is 72°, find the angle of incidence.
i = r
i = 72°
i = 72°
Numerical 5:
A ray makes 40° with the normal. Find the angle between the incident and reflected rays.
i = 40°
r = 40°
Angle between incident and reflected rays:
i + r = 40° + 40°
= 80°
r = 40°
Angle between incident and reflected rays:
i + r = 40° + 40°
= 80°
28. Diagram Labelling Practice
Labels:
A = Incident Ray
B = Reflected Ray
C = Normal
D = Point of Incidence
i = Angle of Incidence
r = Angle of Reflection
B = Reflected Ray
C = Normal
D = Point of Incidence
i = Angle of Incidence
r = Angle of Reflection
29. CBSE Golden Points ⭐
- Reflection means return of light into the same medium.
- The incident ray, reflected ray and normal lie in the same plane.
- Angle of incidence is measured from the normal.
- Angle of reflection is measured from the normal.
- Second law: i = r.
- For normal incidence, i = r = 0°.
- A normally incident ray retraces its path.
- Mirror surface and normal are perpendicular.
- Angle with mirror + angle with normal = 90°.
- Diffuse reflection does not violate the laws of reflection.
- Each individual ray follows i = r.
- Regular reflection occurs on smooth surfaces.
- Diffuse reflection occurs on rough surfaces.
- The angle between incident and reflected rays is 2i.
- Always draw the normal before measuring the angle.
30. Memory Tricks 🧠
First Law:
I + R + N = Same Plane
I = Incident Ray
R = Reflected Ray
N = Normal
I + R + N = Same Plane
I = Incident Ray
R = Reflected Ray
N = Normal
Second Law:
“I = R”
Incidence = Reflection
i = r
“I = R”
Incidence = Reflection
i = r
Angle Trick:
Mirror + Normal = 90°
Therefore:
Angle with Normal = 90° − Angle with Mirror
Mirror + Normal = 90°
Therefore:
Angle with Normal = 90° − Angle with Mirror
Normal Incidence:
Normal → Zero → Same Path
i = 0° → r = 0° → ray returns on same path.
Normal → Zero → Same Path
i = 0° → r = 0° → ray returns on same path.
31. One-Line Revision
Incident Ray + Reflected Ray + Normal → Same Plane
Angle of Incidence = Angle of Reflection
i = r
Angle with Mirror + Angle with Normal = 90°
32. Final Summary | अंतिम सारांश
Laws of Reflection प्रकाश के परावर्तन को समझने के लिए सबसे महत्वपूर्ण नियम हैं।
First Law: आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में होते हैं।
Second Law: आपतन कोण परावर्तन कोण के बराबर होता है।
यदि कोण mirror surface से दिया हो तो:
इस chapter में numerical problems, ray diagrams और experimental verification के लिए इन concepts का सही उपयोग अत्यंत महत्वपूर्ण है।
First Law: आपतित किरण, परावर्तित किरण और अभिलम्ब एक ही तल में होते हैं।
Second Law: आपतन कोण परावर्तन कोण के बराबर होता है।
i = r
Normal incidence में:
i = r = 0°
और ray अपने उसी path पर वापस लौटती है।
यदि कोण mirror surface से दिया हो तो:
Angle with Normal = 90° − Angle with Mirror
इस chapter में numerical problems, ray diagrams और experimental verification के लिए इन concepts का सही उपयोग अत्यंत महत्वपूर्ण है।
🔦 Laws of Reflection
Class 10 Science | Light – Reflection and Refraction
Understand → Visualise → Practise → Master
