Class 10 Science – Light Reflection and Refraction | Interactive Visual Revision Notes

1. Classroom Notes

Real-world connection: When you look into a still pond, you see your own reflection — that is reflection of light. When you place a straw in a glass of water and it appears bent at the surface — that is refraction. Every bathroom mirror, car rear-view mirror, and magnifying glass works because of the laws in this chapter.

What is Light?

Light lets us see things around.
Light travels in straight lines always.
Light moves very very fast.
Light bounces off shiny surfaces.
Light bends when entering new material.

Laws of Reflection

Light hits a mirror and bounces.
The incoming ray is called incident.
The bouncing ray is called reflected.
Angle of incidence equals angle of reflection.
Normal is a line perpendicular to mirror.

Concave Mirrors

Concave mirrors curve inward like a bowl.
They can make images bigger.
Dentists use concave mirrors to see.
Headlights use concave mirrors too.
They focus light to one point.

Convex Mirrors

Convex mirrors curve outward like a ball.
They make things look smaller.
Car side mirrors are convex.
They show a wider view.
Image is always upright and smaller.

Mirror Formula

Formula is 1/v + 1/u = 1/f.
v is image distance from mirror.
u is object distance from mirror.
f is focal length of mirror.
This helps find where image forms.

Refraction of Light

Light bends when it changes material.
Going into water, light slows down.
Slower speed makes light bend.
A pencil looks bent in water.
This bending is called refraction.

Refractive Index

Each material bends light differently.
Glass bends light more than water.
Refractive index tells how much bending.
Higher number means more bending happens.
Diamond has a very high refractive index.

Convex Lens

Convex lens is thick in the middle.
It brings light rays together.
Magnifying glass is a convex lens.
It makes things look bigger.
Camera uses convex lens to focus.

Concave Lens

Concave lens is thin in the middle.
It spreads light rays apart.
It makes things look smaller.
Used in glasses for short sight.
Image is always upright and smaller.

Lens Formula and Power

Lens formula is 1/v - 1/u = 1/f.
Power of lens is 1/f.
Power is measured in dioptres (D).
Thick lens has more power.
Doctor checks your eye's lens power.

3. Worked Examples

Example 1: Find Focal Length

An object is 30 cm from a mirror. The image forms at 15 cm. Find focal length.

1 Use formula: 1/v + 1/u = 1/f

2 Put values: 1/(-15) + 1/(-30) = 1/f

3 Solve: -1/15 - 1/30 = -3/30 = -1/10

Answer: f = -10 cm (concave mirror)

Example 2: Find Image Distance (Lens)

Object is at 20 cm from convex lens. Focal length is 10 cm. Find image.

1 Use formula: 1/v - 1/u = 1/f

2 Put values: 1/v - 1/(-20) = 1/10

3 Simplify: 1/v + 1/20 = 1/10

4 Solve: 1/v = 1/10 - 1/20 = 1/20

Answer: v = 20 cm on other side

Example 3: Find Power of Lens

Focal length is 25 cm = 0.25 m. Find power.

1 Use formula: Power = 1/f

2 Put value: P = 1 / 0.25

3 Calculate: P = 4

Answer: Power = +4 D (convex lens, positive)

4. Cheat Sheet

Term	Meaning
Reflection	Light bouncing off a surface
Refraction	Light bending in a new material
Incident Ray	Light ray going toward mirror
Reflected Ray	Light ray bouncing back
Normal	Line perpendicular to the surface
Concave Mirror	Mirror curving inward like bowl
Convex Mirror	Mirror curving outward like ball
Focal Length	Distance from mirror to focus point
Convex Lens	Thick in middle, brings light together
Concave Lens	Thin in middle, spreads light apart
Refractive Index	Number showing how much light bends
Dioptre	Unit to measure lens power

5. Take-Home Handout

Part A: Fill in the Blanks

1. Light travels in __________ lines.

2. Angle of incidence equals angle of __________.

3. A concave mirror curves __________ like a bowl.

4. Light bending in a new material is __________.

5. Power of a lens is measured in __________.

Part B: True or False

1. Light always travels in curved lines.

2. A convex mirror makes images bigger.

3. Refraction happens when light changes material.

4. A concave lens is thick in the middle.

5. Diamond has a high refractive index.

Part C: Solve These Problems

1. Object is 40 cm from a concave mirror. Image forms at 20 cm. Find focal length.

2. Convex lens has focal length 15 cm. Object at 30 cm. Find image distance.

3. A lens has focal length 50 cm. Find its power in dioptres.

Part D: Match the Columns

Column A	Column B
1. Concave mirror	a. Spreads light rays apart
2. Convex mirror	b. Thick in the middle
3. Convex lens	c. Used in car side mirrors
4. Concave lens	d. Curves inward like a bowl
5. Refractive index	e. Shows how much light bends

Write your answers: 1-__, 2-__, 3-__, 4-__, 5-__

Part E: Draw and Label

Draw a ray diagram for a convex lens. Show the object, image, focus (F), and optical center (O).

✅ Detailed Solutions – Section 5 Handout

Part A: Fill in the Blanks

1 Light travels in straight lines.

2 Angle of incidence equals angle of reflection.

3 A concave mirror curves inward like a bowl.

4 Light bending in a new material is called refraction.

5 Power of a lens is measured in dioptres (D).

Part B: True or False

1 False. Light always travels in straight lines, not curved.

2 False. A convex mirror makes images smaller and upright, not bigger.

3 True. Refraction occurs whenever light moves from one material to another.

4 False. A concave lens is thin in the middle, not thick.

5 True. Diamond has one of the highest refractive indices of any natural material.

Part C: Solved Problems

Problem 1 — Object 40 cm, image 20 cm from a concave mirror. Find focal length.

1 Both object and image are in front of the mirror, so u = −40 cm and v = −20 cm.

2 Use mirror formula: 1/f = 1/v + 1/u.

3 1/f = 1/(−20) + 1/(−40) = −2/40 − 1/40 = −3/40.

f = −40/3 ≈ −13.3 cm (concave mirror, negative focal length).

Problem 2 — Convex lens f = 15 cm, object at 30 cm. Find image distance.

1 Object is on the left, so u = −30 cm. f = +15 cm.

2 Lens formula: 1/v − 1/u = 1/f.

3 1/v − 1/(−30) = 1/15 → 1/v + 1/30 = 1/15.

4 1/v = 1/15 − 1/30 = 2/30 − 1/30 = 1/30.

v = 30 cm. Image forms 30 cm on the other side of the lens (real, inverted, same size).

Problem 3 — Lens with focal length 50 cm. Find power.

1 Convert: f = 50 cm = 0.50 m.

2 P = 1/f = 1/0.50 = 2.

Power = +2 D (positive, so it is a convex lens).

Part D: Match the Columns

1 Concave mirror → d. Curves inward like a bowl

2 Convex mirror → c. Used in car side mirrors

3 Convex lens → b. Thick in the middle

4 Concave lens → a. Spreads light rays apart

5 Refractive index → e. Shows how much light bends

Part E: Ray Diagram – Convex Lens (Description)

1 Draw a horizontal principal axis. Place a convex lens (ellipse) at the centre point O.

2 Mark F on both sides of the lens at equal focal length distances. Mark 2F further out.

3 Place an upward arrow (object) beyond 2F on the left.

4 Ray 1: parallel to axis → bends through F on the right. Ray 2: through optical centre O → goes straight.

Where the two rays meet on the right side is the image location — real and inverted.

6. Revision Flashcards

What is Reflection?

Light bouncing off a shiny surface.

What is Refraction?

Light bending when it enters new material.

What is a Concave Mirror?

A mirror that curves inward like a bowl.

What is a Convex Mirror?

A mirror that curves outward like a ball.

What is Focal Length?

Distance from mirror or lens to focus point.

What is a Convex Lens?

Thick in middle. It brings light rays together.

What is a Concave Lens?

Thin in middle. It spreads light rays apart.

What is Refractive Index?

A number that tells how much light bends.

Light – Reflection and Refraction

Table of Contents

1. Classroom Notes

What is Light?

Laws of Reflection

Concave Mirrors

Convex Mirrors

Mirror Formula

Refraction of Light

Refractive Index

Convex Lens

Concave Lens

Lens Formula and Power

2. Easy Illustrations

Fig 1: Reflection of Light

Fig 2: Concave vs Convex Mirror

Fig 3: Refraction of Light

Fig 4: Convex Lens Ray Diagram

Fig 5: Concave Lens Ray Diagram

3. Worked Examples

Example 1: Find Focal Length

Example 2: Find Image Distance (Lens)

Example 3: Find Power of Lens

4. Cheat Sheet

5. Take-Home Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solve These Problems

Part D: Match the Columns

Part E: Draw and Label

✅ Detailed Solutions – Section 5 Handout

Part A: Fill in the Blanks

Part B: True or False

Part C: Solved Problems

Part D: Match the Columns

Part E: Ray Diagram – Convex Lens (Description)

6. Revision Flashcards

7. Mind Map