Chapter 10 – Light: Mirrors And Lenses (Class 8 Science

🧭 Chapter Overview

Light plays a vital role in our daily life — from the reflection you see in a mirror every morning to the lenses in your spectacles or camera. This chapter, “Light: Mirrors and Lenses,” introduces you to the fascinating science of how light interacts with surfaces and materials.

You’ll learn about different mirrors (plane, concave, convex), how lenses bend light, and how real-world devices like car mirrors, eyeglasses, and telescopes work.

By the end of this lesson, you’ll see how physics and daily life beautifully reflect one another — quite literally!

🎯 Learning Objectives (NEP 2025 Competency Table)

Competency	Learning Outcome	NEP Skill
Conceptual Understanding	Explain laws of reflection and refraction	Conceptual Clarity
Analytical Thinking	Differentiate between concave and convex mirrors/lenses	Critical Analysis
Application	Apply concepts to real-world uses (mirrors, telescopes, eyeglasses)	Practical Knowledge
Experimentation	Observe and record image formation	Inquiry & Scientific Method
Values Integration	Recognize India’s ancient optical knowledge	Cultural Awareness

🌟 10.1 What Are Spherical Mirrors?

Hold a shiny spoon near your face — you’ll see two different kinds of reflections:

The inner curve gives an inverted and enlarged image.
The outer curve gives a small, upright image.

That’s because the spoon acts as a spherical mirror — a mirror shaped like a part of a hollow sphere.

🪞 Types of Spherical Mirrors

Type	Reflecting Surface	Appearance	Example
Concave Mirror	Curved inward (like a cave)	Enlarges objects when close	Shaving mirror, dentist’s mirror
Convex Mirror	Curved outward	Shows smaller, wider images	Car side-view mirror

⚙️ Real-Life Connection

Concave mirrors concentrate light — used in torches, car headlights, and solar cookers.
Convex mirrors spread light — used as rear-view mirrors and safety mirrors in stores and roads.

Did You Know?
Convex mirrors in vehicles carry the message —

“Objects in mirror are closer than they appear.”
That’s because convex mirrors form smaller, distant-looking images while showing a wider field of view.

🌈 10.2 How Do Mirrors Form Images?

The shape of a mirror determines how it reflects light and forms an image.

Concave Mirror:

Object near mirror → Image enlarged, upright.
Object far → Image inverted and smaller.

Convex Mirror:

Image always upright, smaller, and virtual.

Mirror Type	Image Nature	Image Size	Image Orientation
Plane	Virtual	Same size	Upright
Concave	Real or virtual	Enlarged or diminished	Upright (close) / Inverted (far)
Convex	Virtual	Diminished	Upright

🧪 Activity Corner

Try This:
Place a candle in front of a concave mirror in a dark room. Move it closer and farther.
→ You’ll see the candle’s image change from large and upright to small and inverted — a visual proof of how image distance affects reflection.

🔍 10.3 Laws of Reflection

All mirrors follow two universal laws of reflection — whether plane, concave, or convex.

1️⃣ Law 1 – Angle of Incidence = Angle of Reflection
(The light ray hits and reflects at equal angles.)

2️⃣ Law 2 – The Incident Ray, Reflected Ray, and Normal All Lie in the Same Plane

Example Experiment:
Shine light from a torch through a slit (using a comb and black paper).
Observe how the reflected beam always obeys these laws — even if you tilt the mirror!

Quantity	Symbol	Definition
Angle of Incidence	i	Between incident ray & normal
Angle of Reflection	r	Between reflected ray & normal

✅ For all mirrors: i=ri = ri=r

🧩 Reflection in Spherical Mirrors

Concave mirrors → Converge light rays (focus them together)
Convex mirrors → Diverge light rays (spread them apart)

This is why concave mirrors can focus sunlight to a point — a concept used in solar furnaces and solar cookers.

☀️ Real-Life Application – Solar Concentrators

Concave mirrors in solar devices reflect and focus sunlight on a small area, generating intense heat used for:

Cooking food (solar cookers)
Melting metals (solar furnaces)
Producing electricity (solar plants)

🔍 10.4 What Are Lenses?

While mirrors reflect light, lenses bend (refract) it.

A lens is a transparent material (usually glass or plastic) with curved surfaces that refract light to form images.

🧪 Types of Lenses

Type	Structure	Function	Example
Convex Lens	Thicker at center, thinner at edges	Converges light rays	Magnifying glass, human eye
Concave Lens	Thinner at center, thicker at edges	Diverges light rays	Used in eyeglasses for near-sightedness

👁️ Everyday Examples

Convex Lens → Magnifying glasses, cameras, telescopes, microscopes.
Concave Lens → Eyeglasses for myopia (short-sightedness).

🔬 10.5 Image Formation Through Lenses

When you look through a convex lens, the object appears enlarged and upright if close, but inverted when far.
Through a concave lens, the image is always upright and smaller.

Lens Type	Image Nature	Size	Orientation
Convex	Real/Virtual	Enlarged or reduced	Erect (near) / Inverted (far)
Concave	Always Virtual	Diminished	Erect

🔥 Activity: Light Beam & Lens Experiment

Shine parallel light beams using a torch and comb.
Direct them through:
- Glass Plate → Light passes straight.
- Convex Lens → Light converges.
- Concave Lens → Light diverges.

This explains why a convex lens is called a converging lens, and a concave lens is a diverging lens.

☀️ Can a Lens Burn Paper?

Yes! A convex lens can focus sunlight to a point, generating enough heat to ignite paper.
This principle is also used in solar magnifiers and lens-based solar cookers.

⚠️ Safety First: Never look directly at the Sun through a lens.

🪶 10.6 Uses of Mirrors and Lenses in Daily Life

Device	Type Used	Function
Shaving Mirror	Concave	Enlarges face for a close shave
Vehicle Rear-view	Convex	Provides wider field of view
Dentist’s Mirror	Concave	Enlarged image of teeth
Magnifying Glass	Convex	Enlarges text or objects
Spectacles	Concave/Convex	Correct vision
Telescope	Concave Mirror + Convex Lens	View distant objects
Camera Lens	Convex	Focuses light to form image

🧬 Our Scientific Heritage

Over 800 years ago, Indian astronomers during Bhāskara II’s era used reflection from water surfaces to measure star positions.
Even without written laws, their instruments reflected an advanced understanding of optics — proof that ancient India contributed deeply to light science.

🧠 HOTS (Higher Order Thinking Skills)

Why does a concave mirror form an inverted image when the object is far away?
Why do convex mirrors show smaller but wider images?
Why is a convex lens used in magnifying glasses but not a concave one?
What happens to the focal point of a mirror when temperature changes?
Why does a pencil appear bent when placed in water?

⚙️ NEP COMPETENCY FRAMEWORK

Learning Domain	Competency	Example Application
Conceptual	Understanding reflection & refraction	Explain mirror images
Analytical	Compare mirror/lens behavior	Object distance analysis
Practical	Conduct light experiments	Verify i = r law
Ethical	Historical appreciation	Bhāskara II optics
Creative	Design project	DIY solar cooker model

📘 Snapshots (Quick Recap)

✅ Concave Mirrors → Converge light, enlarge or invert images
✅ Convex Mirrors → Diverge light, always form small, erect images
✅ Laws of Reflection → i = r, all rays lie in one plane
✅ Convex Lenses → Converging lenses (used in eyes, cameras)
✅ Concave Lenses → Diverging lenses (used in spectacles)
✅ Ancient India’s Optics → Bhāskara II’s reflective astronomy

⚠️ Exam Alert Box

❗ Frequently Asked 3-Mark Question:
Explain how convex and concave mirrors differ in image formation and give one use of each.

❗ Remember:
Laws of reflection apply to all mirrors — plane, concave, and convex.

💡 Memory Booster Box

🔹 Concave = Converge (mirror)
🔹 Convex = Diverge (mirror)
🔹 Convex lens = Converge light
🔹 Concave lens = Diverge light
🔹 Law: i = r
🔹 Solar devices use concave mirrors and convex lenses.

🔗 INTERNAL & EXTERNAL LINKS

Internal Links (A2ZLY):

External Links:

Chapter 10 – Light: Mirrors and Lenses (Class 8 Science | NEP 2025 Pattern)