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Reflection

Reflection is the bouncing back of light into the same medium after it strikes a surface.

In one line: Bounce back, same medium, same angle from the normal.

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Understand it

When light falls on a smooth surface like a mirror, polished metal, or calm water, it returns back instead of entering the second medium. That return of light is called reflection, and it is the basic reason we see our image in a mirror.

Example

Sunlight falling on a calm lake can produce a bright reflected image of trees or buildings.

Formula and rule

Reflection follows the basic idea that the angle of incidence equals the angle of reflection, measured from the normal.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1A light ray falls on a shining tray and returns at the same angle.
  2. 2If it makes 30° with the normal before hitting the tray, it also makes 30° after reflection.

Method you can reuse

  1. 1Check whether light stays in the same medium.
  2. 2See if it bounces from a smooth surface.
  3. 3Name the process as reflection.

Sketch it in your answer

Draw the incident ray, reflected ray, point of incidence, and normal; mark equal angles on both sides of the normal.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why do you see your face in a plane mirror instead of the mirror absorbing the light?

Think first, then show answer
You see your face because the mirror reflects light from your face back to your eyes; it does not absorb the light completely.

Common wrong answer

Saying refraction because the ray changes direction. This is wrong when the ray simply bounces back in the same medium.

Don't mix this up

Students often think the light enters the surface and changes medium, but reflection keeps light in the same medium.

Exam tip

If the ray returns after striking a smooth surface, write reflection; if it bends into a new medium, write refraction.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Students may be asked to identify the process, explain image formation in a mirror, or draw the reflected ray.
  1. 1

    Enough for 1 mark

    Reflection is the bouncing back of light into the same medium after it strikes a surface.

  2. 2

    Add for 2 marks

    Example: Sunlight falling on a calm lake can produce a bright reflected image of trees or buildings.

  3. 3

    Add for 3 marks

    When light falls on a smooth surface like a mirror, polished metal, or calm water, it returns back instead of entering the second medium.

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