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Tamil Nadu (TNBSE)Class 8 Science★ 4-7 marks in the TN Class 8 annual exam through book-back MCQs, fill-ups and short answers

Light

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 3, Light. Luminous and non-luminous objects, regular and irregular reflection and the laws of reflection, multiple reflection (periscope, kaleidoscope), refraction, and the dispersion of white light (VIBGYOR). Notes with the actual book-back questions, worked examples, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Distinguish luminous and non-luminous objects
2State and apply the laws of reflection
3Distinguish regular and irregular reflection
4Explain multiple reflection (periscope, kaleidoscope)
5Explain refraction and dispersion

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Why this chapter matters

Light explains why we see objects, how mirrors and the periscope work, and why rainbows form. Luminous/non-luminous objects, the laws of reflection and dispersion are directly tested book-back content in the TN Class 8 exam.

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A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 7 — Light

Light travels in straight lines; shadows.

Light — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Physics — Chapter 3. How light reflects, bends and splits into colours.

1. About this chapter

This chapter covers luminous and non-luminous objects, reflection and its laws, multiple reflection, refraction, and the dispersion of light.

2. Luminous and non-luminous objects

Luminous objects give out their own light (the Sun, a lamp, a candle).
Non-luminous objects do not give out light; they are seen because they reflect light (the Moon, a table, a book).

3. Reflection of light

Reflection is the bouncing back of light from a surface.
Laws of reflection: (1) the angle of incidence = angle of reflection; (2) the incident ray, reflected ray and normal lie in the same plane.
Regular reflection (from a smooth surface like a mirror) gives a clear image; irregular (diffused) reflection (from a rough surface) scatters the light.

4. Multiple reflection, refraction and dispersion

Multiple reflection: the periscope uses two mirrors (at 45°) to see over obstacles; the kaleidoscope uses mirrors to form symmetric patterns.
Refraction: the bending of light as it passes from one medium to another (a pencil looks bent in water).
Dispersion: white light splits into seven colours — VIBGYOR — when it passes through a prism; this is why a rainbow forms.

5. Worked examples

Example 1. Is the Moon a luminous or non-luminous object? Non-luminous — it shines by reflecting the Sun's light.

Example 2. A ray strikes a mirror at 30° to the normal. Find the angle of reflection. By the law of reflection, 30°.

Example 3. Why does a pencil look bent in water? Because of refraction — light bends as it moves from water to air.

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

An object that gives out its own light is — (a) luminous / (b) non-luminous. Ans: (a) luminous.
Reflection from a smooth surface is — (a) regular / (b) irregular. Ans: (a) regular.
The splitting of white light into seven colours is — (a) reflection / (b) dispersion. Ans: (b) dispersion.
The instrument that uses two mirrors to see over obstacles is the — (a) periscope / (b) telescope. Ans: (a) periscope.

II. Fill in the blanks 5. The angle of incidence is equal to the angle of reflection. 6. The seven colours of white light are remembered as VIBGYOR. 7. The Moon is a non-luminous object.

III. Answer briefly 8. State the laws of reflection. 9. Differentiate luminous and non-luminous objects with examples.

7. Common mistakes

Mistake: Calling the Moon a luminous object. Fix: The Moon is non-luminous; it reflects sunlight.
Mistake: Measuring angles from the mirror instead of the normal. Fix: Angles of incidence and reflection are measured from the normal.
Mistake: Confusing reflection and refraction. Fix: Reflection = bouncing back; refraction = bending while passing through.

8. Quick revision

Physics Ch 3 · luminous/non-luminous, reflection, refraction, dispersion.
Luminous (own light: Sun, lamp) vs non-luminous (reflect: Moon, table).
Laws of reflection: i = r; rays and normal coplanar.
Regular (smooth) vs irregular (rough) reflection; periscope and kaleidoscope.
Refraction = bending between media; dispersion → VIBGYOR (rainbow).

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Luminous vs non-luminous

own light vs reflected light

Sun vs Moon.

Law of reflection

angle of incidence = angle of reflection

Measured from the normal.

Dispersion

white light → VIBGYOR by a prism

Seven colours; rainbow.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Calling the Moon a luminous object

✓ The Moon is non-luminous; it reflects sunlight.

WATCH OUT

✗ Measuring angles from the mirror instead of the normal

✓ Angles of incidence and reflection are measured from the normal.

WATCH OUT

✗ Confusing reflection and refraction

✓ Reflection = bouncing back; refraction = bending while passing through.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on luminous objects, reflection and dispersion.

Questions

Fill in the blanks

Angle of reflection, VIBGYOR and non-luminous objects.

Questions

Answer briefly / in detail

Laws of reflection, luminous vs non-luminous, the periscope.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

An object that gives out its own light is (a) luminous (b) non-luminous.

▶ Show solution

(a) luminous.

Q2EASY· MCQ

The splitting of white light into seven colours is called ____.

▶ Show solution

dispersion.

Q3EASY· Fill in the blanks

The Moon is a ____ object.

▶ Show solution

non-luminous.

Q4EASY· Answer briefly

State the laws of reflection.

▶ Show solution

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

Q5EASY· Answer briefly

Differentiate luminous and non-luminous objects with examples.

▶ Show solution

Luminous objects give out their own light (Sun, lamp); non-luminous objects are seen by reflecting light (Moon, table).

Q6EASY· Numerical

A ray strikes a mirror at 30° to the normal. Find the angle of reflection.

▶ Show solution

30° (angle of incidence = angle of reflection).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Physics Chapter 3 of Samacheer Kalvi Class 8 Science.
•Luminous (own light: Sun, lamp) vs non-luminous (reflect: Moon, table).
•Laws of reflection: i = r; rays and normal coplanar.
•Regular (smooth) vs irregular (rough) reflection.
•Periscope and kaleidoscope use multiple reflection.
•Refraction = bending between media; dispersion → VIBGYOR (rainbow).

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4-7 marks across book-back MCQ, fill-ups and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Fill	1	3-4	Luminous objects, reflection, dispersion
Short Answer	2-3	1-2	Laws of reflection, refraction
Diagram	2	0-1	Periscope / ray diagram

Prep strategy

Separate luminous and non-luminous objects
Learn the laws of reflection
Memorise VIBGYOR
Know the periscope and kaleidoscope

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Mirrors and periscopes

Reflection is used in mirrors, periscopes and vehicle mirrors.

Optical instruments

Refraction is used in lenses, cameras and spectacles.

Rainbows

Dispersion explains rainbows and prism colours.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Classify objects as luminous/non-luminous
Measure reflection angles from the normal
Recall VIBGYOR for dispersion
Label ray diagrams neatly

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Find the number of images formed by two mirrors at 60°.
Explain why the sky appears blue (scattering).

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

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Questions students ask

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Because they reflect the light falling on them from a luminous source into our eyes.

Sunlight is refracted and dispersed by tiny water droplets, splitting into its seven colours (VIBGYOR).

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