# Refraction

In this worksheet, students will explore how light changes direction at the boundaries of two different substances and this creates effects, such as mirages.

Key stage:  KS 3

Curriculum topic:   Physics: Waves

Curriculum subtopic:   Light Waves

Difficulty level:

### QUESTION 1 of 10

When light goes through different transparent substances, it appears to bend or change direction; for example, when it goes from air to water or vice versa. This phenomenon is called refraction. Refraction happens at the interface of two substances, i.e. where the substances meet (their boundaries). However, if light passes through the interface vertically (at a 90 degree angle), refraction does not occur. The straw in the picture below looks broken because of refraction. Additionally, on sunny days, it looks like there is water on the road ahead when travelling by car; this is also due to refraction and it is called mirage.

Water or glass are more dense materials than air, so light slows down when it travels from air into glass or water, and it speeds up when it enters air from glass or water. The diagram below is essential to understanding refraction of light, so study it carefully.

The green and red lines show the speed and direction of light in air and water, whereas the dotted line needs to be drawn on the diagram by us, so we can calculate the angles of incidence: A and C (when light hits the different medium) and the angles of refraction, B and D (when light comes out of the interface). In the first diagram, A is bigger than B (A > B), because water is denser than air. In the second diagram, D is bigger than C (D > C), because air is less dense than water, so light speeds up when it enters air.

Type the scientific word used when light bends (changes direction).

What happens when light goes from one medium to another that is denser than the first; for example, from air to water?

it slows down

it speeds up

nothing

What happens to the speed of light when it travels from glass into air?

it decreases

it increases

it remains the same

What happens when light enters glass from air at 90 degrees?

it slows down

it speeds up

nothing

Above is the picture of a straw in a glass of water. It looks like the straw is broken. Why is that?

Tick two boxes.

It is because of refraction of light.

It is really broken.

It bends because water pushes it.

Light slows down when it enters the water, so it is reflected from a different position to our eyes.

What do we call the phenomenon of seeing water on a road ahead of us on a sunny day?

What is the dotted line on the second diagram in the intro called?

Why is it necessary to draw the normal on diagrams of refraction?

because it's a light ray

because it helps us measure the angles of incidence and refraction

to make everything look straight

Which angle is bigger when light enters air from water?

angle of incidence

angle of refraction

they are equal

Which angle is smaller when light travels from glass to air?

angle of incidence

angle of refraction

they are the same

• Question 1

Type the scientific word used when light bends (changes direction).

refraction
EDDIE SAYS
Light changes direction when it enters different mediums. This is called refraction.
• Question 2

What happens when light goes from one medium to another that is denser than the first; for example, from air to water?

it slows down
EDDIE SAYS
Light would slow down when travelling from air into water, because water is denser than air. However, if it enters water at 90 degrees, the speed of light would remain the same, but this is not specified in the third option, so it is not correct.
• Question 3

What happens to the speed of light when it travels from glass into air?

it increases
EDDIE SAYS
Light would slow down when travelling from air into water, because water is denser than air. This means that it would speed up (increase in speed) when it travels from glass into air.
• Question 4

What happens when light enters glass from air at 90 degrees?

nothing
EDDIE SAYS
Light would slow down when travelling from air into water, because water is denser than air. However, if it enters water at 90 degrees, the speed of light would remain the same.
• Question 5

Above is the picture of a straw in a glass of water. It looks like the straw is broken. Why is that?

Tick two boxes.

It is because of refraction of light.
Light slows down when it enters the water, so it is reflected from a different position to our eyes.
EDDIE SAYS
Light would slow down when travelling from air into water, because water is denser than air. This is called refraction. We see because light is reflected back to our eyes from a different position.
• Question 6

What do we call the phenomenon of seeing water on a road ahead of us on a sunny day?

mirage
a mirage
EDDIE SAYS
On sunny days it looks like there is water on the road ahead. This is due to refraction of light and it is called a mirage.
• Question 7

What is the dotted line on the second diagram in the intro called?

normal
EDDIE SAYS
The dotted line on refraction diagrams is called normal.
• Question 8

Why is it necessary to draw the normal on diagrams of refraction?

because it helps us measure the angles of incidence and refraction
EDDIE SAYS
The normal helps in measuring the angles of incidence and refraction.
• Question 9

Which angle is bigger when light enters air from water?

angle of refraction
EDDIE SAYS
Air is less dense than water so light speeds up and moves away from the normal, making the angle of refraction bigger than that of incidence.
• Question 10

Which angle is smaller when light travels from glass to air?

angle of incidence
EDDIE SAYS
Air is less dense than glass so light speeds up and moves away from the normal, making the angle of incidence smaller than that of refraction.
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