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Light, shadows and reflection

Learn how light travels in straight lines, why objects make shadows, and how a mirror reflects light and flips left and right.

Get the whole book: Science for classes 6 to 8 (4 lessons, free to print)

Let us begin

The big idea

We see a mango because light bounces off it and enters our eyes. Light also makes shadows and helps us see ourselves in a mirror. Let us look at how light behaves.

Objects that give out their own light, like the Sun, a flame and a torch, are called luminous. Objects like a book or a chair do not give out light. We see them only when light from another source falls on them and bounces into our eyes.

Light travels in straight lines. You cannot see around a corner for this reason.

Materials are of three kinds. Transparent materials let almost all light pass through, like clear glass. Translucent materials let some light pass, like butter paper. Opaque materials let no light pass, like wood, metal and cardboard.

A shadow forms when an opaque object blocks light. The shadow is the dark space behind the object, where the light cannot reach. A shadow is bigger when the object is nearer the light source and smaller when it is farther away.

When light falls on a smooth shiny surface like a mirror, it bounces back. This is reflection. In a plane (flat) mirror, the angle of incidence is equal to the angle of reflection. Both angles are measured from the normal, an imaginary line at right angles to the mirror. The image in a plane mirror is the same size as the object, but left and right are swapped. This is called lateral inversion. That is why the word AMBULANCE is printed reversed on the front of an ambulance, so that drivers see it correctly in their mirrors.

How a shadow formsA light source on the left sends straight rays to the right. An opaque object in the middle blocks the central rays. On the wall on the right, a dark patch called the shadow appears where the light is blocked, with lit areas above and below it. Light source Opaque object Wall Shadow
Light travels in straight lines. An opaque object blocks it and leaves a shadow.

Worked examples

See how it works

  1. Transparent, translucent or opaque?

    A clear glass window is transparent. Butter paper is translucent: you can see a blurry shape through it. A wooden door is opaque: you cannot see through it at all.

  2. Reflection angles

    A ray of light hits a plane mirror at an angle of incidence of 40°. By the law of reflection, the angle of reflection is also 40°. The angle between the incoming ray and the reflected ray is 40° + 40° = 80°.

  3. Size of a shadow

    You hold a toy near a lit torch and the shadow on the wall is large. You move the toy towards the wall, away from the torch, and the shadow becomes smaller.

Try it at home

Shadow play and see-through test

You will need

  • A torch
  • A plain wall in a dim room
  • A cardboard cut-out or a toy
  • Butter paper or thin paper
  • A clear plastic bag or glass
  • A flat mirror

What to do

  1. In a dim room, shine the torch on the wall and hold the toy between the torch and the wall.
  2. Move the toy closer to the torch, then closer to the wall. Notice how the shadow size changes.
  3. Hold butter paper, clear plastic and cardboard one at a time in front of the torch. Which ones let light through?
  4. Write down: transparent, translucent or opaque.
  5. Hold a word in front of a mirror and see how it is flipped left to right.

Ask a grown-up: Do the activity indoors with a torch. NEVER look at the Sun or shine a torch or laser straight into anyone's eyes.

Fun fact

Light travels about 3 lakh kilometres in one second.

Practice sheet

Check what you learned

Write your answers in a notebook, or print this sheet and write on it. When you finish, mark your work with the answer key.

Practice sheet: Light, shadows and reflection (Classes 6-8, Science)

  1. Name one luminous object.
  2. In what kind of path does light travel?
  3. Is clear glass transparent, translucent or opaque?
  4. Is butter paper transparent, translucent or opaque?
  5. What type of material forms a clear, dark shadow: transparent or opaque?
  6. What happens to the size of a shadow when you move the object nearer to the torch?
  7. What do we call the bouncing back of light from a mirror?
  8. A ray of light hits a mirror with an angle of incidence of 35°. What is the angle of reflection?
  9. The angle of incidence is 50°. What is the angle between the incident ray and the reflected ray?
  10. Why is the word AMBULANCE written reversed on the front of an ambulance?

Answer key

Answers: Light, shadows and reflection

Do the practice sheet first, then check here. If an answer is different from yours, read the lesson again and try once more.

  1. Any one of the Sun, a flame, a torch or a lit bulb.
  2. In straight lines.
  3. Transparent.
  4. Translucent.
  5. Opaque.
  6. The shadow becomes bigger.
  7. Reflection.
  8. 35°, because the angle of reflection equals the angle of incidence.
  9. 50° + 50° = 100°.
  10. A mirror swaps left and right, so a driver looking in the mirror reads the word correctly.

What next

Keep learning

Get the whole book

All 4 science lessons for classes 6 to 8 on one page, with every practice sheet and answer key, ready to print.

Science for classes 6 to 8

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