Refraction February 2023
Key words Challenge Practise Try
What happens to light rays What is the difference What is the law of
when light meets: between specular reflection?
● Lenses
A) Transparent materials reflection and diffuse
● Refraction
●
B) Translucent materials reflection?
Interface
● Converging lens C) Opaque materials
● Focal length
● Focal point
L.O: Use a model to explain how lenses work.
What is refraction?
Explaining refraction
Light waves change speed when they pass across the interface (the boundary) between two
substances with a different density, such as air and glass.
● This causes them to change direction, an effect called refraction.
At the boundary between two transparent substances:
● the light slows down going into a denser substance, and the ray bends towards the normal
● the light speeds up going into a less dense substance, and the ray bends away from the normal
PRACTISE
Understanding
refraction
Drawing and labelling
The material that lightrefraction
is travelling through is called a medium.
When light strikes a surface, we can describe how it behaves by
comparing it to the “normal” line. This is a line we draw at right angles
to the surface, where the light hits it.
If light travels from a less dense medium into a
denser medium, it changes direction toward
the normal.
If light travels from a denser medium into a less
dense medium, it changes direction away
from the normal line.
Rays of light were measured being refracted travelling
from air into a block of glass. Use the information in the
table and the diagram to fill in the missing words.
Light is only refracted if it enters glass at an _______.
The angle of incidence is always __________ the angle of refraction.
When entering the block, the ray bends _______ the normal.
The angle at which light leaves the block is ________ the angle it
enters the block.
the same as angle towards
greater than
Cars and sand
1 a What happens to the speed of a toy car when it
rolls into a patch of sand, as shown on the right?
_________________________________________
b What happens to the direction in which the
car is travelling?
_________________________________________
2 a Describe what will happen to the direction of
the car if it travels into the sand, as shown on
the right.
_________________________________________
b Explain why this happens.
_________________________________________
Converging Lenses
Light can be focused so that the rays appear to meet at a single point.
→ Focusing light is important for getting clear images in our eye or in photographs,
because images that are not focused appear blurred.
A lens is a specially shaped pieces of glass or transparent plastic.
→ Lens are used to focus or disperse light.
A convex lens is made from a transparent material that bulges outwards in the
middle on both sides. Convex lenses are used to converge light to a single point.
→ Light is refracted as it passes into, then out of, the lens.
1)
A.
B.
C.
2)
Converging Lenses
Focal length - the distance between the centre of the lens and the focal point.
Focal point - the point where the refracted light rays meet.
Converging Lenses
6)
8)
TRY
Questions
Questions PRACTISE
