PhysicsICSE Class 8 · Light Energy

Refraction and Dispersion of Light: Bending, Prism and Spectrum (ICSE Class 8 Physics)

Updated 17 October 2026 · Fact-checked

Refraction is the bending of light when it passes obliquely from one transparent medium into another, because its speed changes: into a denser medium it bends towards the normal, out of it away from the normal. Dispersion is the splitting of white light by a prism into the seven colours VIBGYOR.

Light bends towards the normal entering water, and a prism bends each colour differently, violet the most and red the least.

Illustration drawn for QuestionBuddy.

Understand Refraction and Dispersion of Light

Refraction. Light travels in a straight line in one transparent medium, but changes direction when it passes obliquely into another (air into water or glass), because it travels at different speeds in different media.

Air to water or glass (denser medium): the ray bends towards the normal.
Water or glass to air: the ray bends away from the normal.
A ray that meets the surface along the normal (at 90° to the surface) goes straight through without bending.

The normal is the line at right angles to the surface at the point where the ray strikes.

Everyday refraction.

A pencil in a glass of water looks bent (or broken) at the surface.
A swimming pool or tank looks shallower than it is: rays from the bottom bend away from the normal on leaving the water, so the bottom seems raised.
A coin at the bottom of a bowl that you cannot see becomes visible when water is poured in.
Stars twinkle: starlight passes through layers of air of varying density, bending by changing amounts.

Dispersion. White light passing through a glass prism splits into seven colours: VIBGYOR (violet, indigo, blue, green, yellow, orange, red). The band of colours is a spectrum. Each colour is bent by a different amount: violet is bent the most, red the least. A rainbow is formed by dispersion of sunlight in raindrops.

White light is therefore a mixture of colours. A second, inverted prism can recombine the colours into white light.

Drawing tips. Draw the normal as a dotted line; mark incident ray, refracted ray, and the angles measured from the normal; put arrows on all rays.

Refraction and Dispersion of Light: formulas and key facts

Bending rule: Air to glass or water towards the normal
Glass or water to air away from the normal
Along the normal no bending; Because light speed changes.
Spectrum (VIBGYOR): $V i o l e t ∣ I n d i g o ∣ B l u e ∣ G r ee n ∣ Y e l l o w ∣ O r an g e ∣ R e d$; Violet bends most, red least.
Examples: Bent pencil
Shallow pool
Twinkling stars
Rainbow; All come from refraction or dispersion.

Air to glass or water	towards the normal
Glass or water to air	away from the normal
Along the normal	no bending

How to solve Refraction and Dispersion of Light questions

Name the two media, decide which is denser, then apply the bending rule.

1Identify the medium the ray enters: denser (glass, water) or rarer (air).
2Entering the denser medium: towards the normal; leaving it: away from the normal.
3Draw the normal first; measure angles from it.
4For a prism, say that violet bends most and red least, giving the spread.

Refraction and Dispersion of Light in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Why the pool looks shallow

Suppose you stand at the edge of a swimming pool and see the floor tiles apparently close to the surface.

Explain why the pool seems shallower than it is.

Try it first, then show the solutionSolution

Light from a tile moves from water into air, bending away from the normal.
The eye traces the rays back in straight lines, so the tile seems to be higher than it really is.

Answer: Refraction at the water surface makes the bottom appear raised.

Memory hook: Leaving water, rays bend away; the floor seems up.

Rainbow after rain

Imagine the Sun shines through fine raindrops after a shower.

Why do you see a band of colours?

Try it first, then show the solutionSolution

Drops act like tiny prisms; sunlight bends on entering and leaving.
Each colour bends by a different amount, giving the spectrum VIBGYOR.

Answer: Dispersion of sunlight in raindrops.

Memory hook: Drops are tiny prisms.

Tricks to remember Refraction and Dispersion of Light

Short memory aids. Say each one aloud once, then use it on a question the same day.

VIBGYOR
Violet, Indigo, Blue, Green, Yellow, Orange, Red: violet bends most.
Use it when: Order of colours.
Dense in, towards
Into a denser medium, bends Towards the normal: "Dense = Draws in".
Use it when: Bending rule.
Bent pencil
The lower part is seen through water, so rays bend and it seems shifted.
Use it when: Everyday example.

Refraction and Dispersion of Light: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Bending into glass · 1 mark · MCQBoard level

A ray of light travelling from air into glass bends:
(a) away from the normal
(b) towards the normal
(c) not at all
(d) along the surface

Try it first, then show the solutionSolution

Glass is denser, so the ray bends towards the normal.

Answer: (b) towards the normal

Example 2: The bent pencil · 2 marks · Short answerBoard level

A pencil in a glass of water appears bent at the surface of the water. Name the phenomenon and explain it in two lines.

Try it first, then show the solutionSolution

Refraction of light. (½)
Light from the part under water bends away from the normal as it enters air, so the eye sees that part shifted and the pencil appears bent. (1½)

Answer: Refraction

Example 3: Through a glass block · 3 marks · Short answerHarder board level

A ray of light meets a rectangular glass block at an angle to the normal. Describe how the ray moves (a) on entering the block, (b) on leaving it. What happens if the ray meets the surface along the normal?

Try it first, then show the solutionSolution

(a) It bends towards the normal on entering (glass is denser). (1)
(b) It bends away from the normal on leaving into air. (1)
Along the normal there is no bending: it passes straight through. (1)

Answer: (a) towards the normal (b) away from the normal; along the normal, undeviated

Example 4: Prism and the spectrum · 3 marks · Short answerHarder board level

A narrow beam of white light falls on a glass prism. (a) Name the effect. (b) Which colour is deviated most and which least? (c) Why do the colours separate?

Try it first, then show the solutionSolution

(a) Dispersion. (1)
(b) Violet most, red least. (1)
(c) Each colour is bent by a different amount in glass, so they separate into a spectrum. (1)

Answer: (a) dispersion (b) violet, red (c) different bending

Example 5: The coin trick · 4 marks · Case-basedHOTS / competency

A coin lies at the bottom of an opaque bowl, just hidden from your eye by the rim. Water is poured in without moving the coin or your eye, and the coin becomes visible. (a) Explain. (b) Name the phenomenon. (c) State the direction of bending of the rays at the water surface. (d) Will the coin appear higher or lower than its real position?

Try it first, then show the solutionSolution

(a) Rays from the coin now bend at the water surface and reach the eye over the rim. (1)
(b) Refraction. (1)
(c) Away from the normal, as they go from water to air. (1)
(d) Higher (raised), because the eye traces the rays back in straight lines. (1)

Answer: (a) refraction at the surface (b) refraction (c) away from the normal (d) higher

Where students lose marks in Refraction and Dispersion of Light

The slips examiners see most often, and what to write instead.

Mistake: Bending the wrong way
The direction depends on which medium the ray enters.
Wrong working
"Light going from air into glass bends away from the normal."
Right working
"Light going from air into glass bends towards the normal."
Do this: Dense in: towards. Dense out: away.
Mistake: Calling refraction reflection
Refraction is bending on entering a new medium, reflection is bouncing back.
Wrong working
"The pencil looks bent due to reflection."
Right working
"The pencil looks bent due to refraction."
Do this: Use the exact words.
Mistake: Wrong colour order
The spectrum follows VIBGYOR.
Wrong working
"Red bends the most, so red is at the most-bent end of the spectrum."
Right working
"Violet bends the most and lies at the most-bent end of the spectrum; red bends the least and lies at the least-bent end."
Do this: Write violet for the most-bent end.

Exam tips

Draw the normal as a dotted line and mark both angles from the normal.
Always add arrows on the rays.
Link every example to the same idea: light changes speed and bends.
Remember: violet bends most, red least.

Practice questions on Refraction and Dispersion of Light

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
What is the bending of light as it passes from one medium to another called?
Hint
Not reflection.
Answer
Refraction.
Q2 · 2 marks · Short answerHarder board level
Why do stars appear to twinkle?
Hint
The air is not uniform.
Answer
Starlight passes through layers of air with varying density; it is bent by changing amounts, so the star seems to flicker.
Q3 · 2 marks · Short answerBoard level
List the colours of the spectrum in order and say which one bends least.
Hint
VIBGYOR.
Answer
Violet, indigo, blue, green, yellow, orange, red; red bends least.
Q4 · 3 marks · Short answerHarder board level
A stick is held slanting in water so that half is submerged. Explain why the submerged half seems raised and the stick appears bent at the water surface. Would a ray from the end of the stick that reaches the surface along the normal be bent?
Hint
Rays leave the water and bend away.
Answer
Rays from the submerged part bend away from the normal on leaving the water, so the eye traces them back to a higher position and the stick seems bent at the surface. A ray that meets the surface along the normal is not bent.
Q5 · 2 marks · Assertion-reasonHOTS / competency
Assertion (A): A ray striking a glass surface along the normal does not bend.
Reason (R): Light travels at the same speed in air and in glass.
(a) A and R true, R explains A
(b) A and R true, R does not explain A
(c) A true, R false
(d) A false, R true
Hint
A change of direction needs an oblique ray.
Answer
A is true: a ray along the normal goes undeviated. R is false: light travels at different speeds in the two media, which is the cause of refraction. So (c).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Cause of refraction?Show answer
Change in the speed of light in the new medium.
2.Air to glass: bends?Show answer
Towards the normal.
3.Colours of the spectrum?Show answer
VIBGYOR.
4.Most-bent colour?Show answer
Violet.
5.A ray along the normal?Show answer
Goes straight, no bending.

Refraction and Dispersion of Light: frequently asked questions

What is refraction of light?

Refraction is the bending of light when it passes obliquely from one transparent medium to another, caused by the change in the speed of light.

Why does a swimming pool look shallower?

Light from the bottom bends away from the normal as it leaves the water, so the eye sees the bottom raised and the pool seems shallower.

What is dispersion of light?

Dispersion is the splitting of white light into its seven colours (VIBGYOR) by a prism, because each colour bends by a different amount.