Chapter 14 of 19

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Tamil Nadu (TNBSE)Class 7 Science★ 6-10 marks in the TN Class 7 Term 3 exam through book-back MCQs, true/false and short answers

Light

Samacheer Kalvi (TN State Board) Class 7 Science — Term 3 Chapter 1, Light. The rectilinear propagation of light and shadows, reflection and the plane mirror image, the pinhole camera and its inverted image, and the dispersion of white light into seven colours by a prism, with the actual book-back questions, common mistakes and quick revision.

⏱ 15 min readEasy difficulty✓ Free · NCERT-aligned

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

1State that light travels in a straight line
2Explain how shadows form and change
3Describe reflection and the plane mirror image
4Explain the pinhole camera image
5Describe the dispersion of white light

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Why this chapter matters

Light explains how we see, how shadows and images form, and why a rainbow has colours. Reflection, the pinhole camera and dispersion are directly tested book-back content in the TN Class 7 Term 3 exam.

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

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Class 6 — Light, Shadows and Reflections

Light and shadows.

Light — Class 7 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 7 Science, Term 3 — Chapter 1. Reflection, shadows and the colours of light.

1. About this chapter

This chapter covers the straight-line travel of light and shadows, reflection and the plane mirror, the pinhole camera, and the dispersion of light.

2. Light travels in a straight line

Light travels in a straight line (rectilinear propagation); it is because of this that shadows are formed and that we can see things only when light reaches our eyes.
We see a book because it reflects the light that falls on it. A shadow is shortest at noon when the Sun is overhead, and longer in the morning and evening.

3. Reflection and the plane mirror

When light hits a mirror, it is reflected. A smooth, shiny mirror surface reflects light well; the plane mirror is the best reflector.
The image in a plane mirror is erect (the same way up), the same size as the object, and laterally inverted (left–right reversed).

4. The pinhole camera and dispersion

A pinhole camera forms an inverted (upside-down) image because light travels in straight lines; the image is not always the same size as the object (it depends on the distances).
Dispersion: when white light passes through a prism, it splits into a band of seven colours (VIBGYOR — violet, indigo, blue, green, yellow, orange, red).

5. Worked examples

Example 1. Why does a pinhole camera form an inverted image? Because light travels in straight lines.

Example 2. Is the image in a plane mirror upside down? No — it is erect (the same way up).

Example 3. How many colours does white light split into through a prism? Seven (VIBGYOR).

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

Shadows are formed because light travels in a — (a) curve / (b) straight line. Ans: (b) straight line.
The best reflector of light is the — (a) plane mirror / (b) wall. Ans: (a) plane mirror.
The image formed by a pinhole camera is — (a) erect / (b) inverted. Ans: (b) inverted.
At noon, the shadow of a vertical stick is — (a) longer / (b) shorter. Ans: (b) shorter.

II. True or False 5. We see a book because it reflects the light that falls on it. — True. 6. The image formed in a pinhole camera is always inverted. — True. 7. The image formed in a pinhole camera is always the same size as the object. — False. 8. The image formed in a plane mirror is upside down. — False (it is erect). 9. After passing through a prism, white light splits into a band of seven colours. — True.

III. Answer briefly 10. State one property of light. — Light travels in a straight line. 11. What is dispersion? — The splitting of white light into seven colours by a prism.

7. Common mistakes

Mistake: Saying the plane mirror image is upside down. Fix: It is erect and the same size, only left–right reversed.
Mistake: Thinking the pinhole image is always the same size. Fix: It is inverted and its size depends on the distances.
Mistake: Saying white light is a single colour. Fix: White light is made of seven colours (seen on dispersion).

8. Quick revision

Term 3 · Ch 1 · light.
Light travels in a straight line → shadows (shortest at noon); we see objects by reflected light.
Plane mirror = best reflector; its image is erect, same size, laterally inverted.
Pinhole camera image = inverted (not always same size); dispersion = white light → seven colours (VIBGYOR).

Key formulas & results

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

Rectilinear propagation

light travels in a straight line

Causes shadows.

Plane mirror image

erect, same size, laterally inverted

Best reflector.

Pinhole camera

inverted image (light travels straight)

Size varies with distance.

Dispersion

white light → seven colours (VIBGYOR)

Through a prism.

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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

✗ Saying the plane mirror image is upside down

✓ It is erect and the same size, only left–right reversed.

WATCH OUT

✗ Thinking the pinhole image is always the same size

✓ It is inverted and its size depends on the distances.

WATCH OUT

✗ Saying white light is a single colour

✓ White light is made of seven colours, seen on dispersion.

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 shadows, the plane mirror, the pinhole image and noon shadows.

Questions

True or False

Reflection, pinhole image and dispersion.

Questions

Answer briefly

Properties of light and dispersion.

Questions

Practice problems

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

Q1EASY· MCQ

Shadows are formed because light travels in a ____.

▶ Show solution

straight line.

Q2EASY· MCQ

The best reflector of light is the ____.

▶ Show solution

plane mirror.

Q3EASY· True/False

True or False: The image formed in a plane mirror is upside down.

▶ Show solution

False — it is erect (only left–right reversed).

Q4EASY· True/False

True or False: The pinhole camera image is always the same size as the object.

▶ Show solution

False — its size depends on the distances.

Q5MEDIUM· Answer briefly

Why does a pinhole camera form an inverted image?

▶ Show solution

Because light travels in straight lines, the rays from the top of the object reach the bottom of the screen and vice versa, so the image is inverted.

Q6MEDIUM· Answer briefly

What is dispersion of light?

▶ Show solution

The splitting of white light into a band of seven colours (VIBGYOR) when it passes through a prism.

5-minute revision

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

•Term 3 Chapter 1 of Samacheer Kalvi Class 7 Science.
•Light travels in a straight line, which forms shadows (shortest at noon).
•We see objects by the light they reflect.
•The plane mirror is the best reflector; its image is erect, the same size and laterally inverted.
•A pinhole camera forms an inverted image because light travels straight; its size varies with distance.
•Dispersion: white light splits into seven colours (VIBGYOR) through a prism.

Tamil Nadu (TNBSE) marks blueprint

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

Typical chapter weightage: 6-10 marks across book-back MCQ, true/false and short answers

Question type	Marks each	Typical count	What it tests
MCQ / True-False	1	5-7	Shadows, mirrors, pinhole, dispersion
Short Answer	2	1-2	Pinhole image, dispersion

Prep strategy

Remember light travels in a straight line
Describe the plane mirror image (erect, same size, reversed)
Explain the inverted pinhole image
Learn the seven colours (VIBGYOR)

Where this shows up in the real world

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

Vision

Reflection lets us see objects and use mirrors.

Photography

The pinhole camera is the basis of all cameras.

Rainbows

Dispersion explains the colours of a rainbow.

Exam strategy

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

Quote 'light travels in a straight line'
Describe the plane mirror image in full
Explain why the pinhole image is inverted
List the seven colours of dispersion

Going beyond the textbook

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

Explain how the size of a pinhole-camera image changes as the object moves closer.
Describe an activity to show that white light is made of seven colours.

Where else this chapter is tested

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

TN Class 7 Term 3 ExamHigh

NMMS / Foundation ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

At noon the Sun is almost directly overhead, so the light strikes a vertical object nearly straight down and the shadow it casts is at its shortest; in the morning and evening the Sun is low, so shadows are long.

A pinhole camera forms a real, inverted (upside-down) image, while a plane mirror forms an erect image of the same size that is reversed left to right.

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