Refraction

Objectives

To find out how light is reflected at a boundary or interface between 2 different materials.

How can we see transparent objects?

Reflection & Refraction

Refraction

Refraction

This diagram shows what happens to light which is reflected by the pencil. The light bends when it leaves the water. Your brain thinks that light always travels in straight lines so the pencil tip seems to be nearer the surface than it really is.

Pencil trickWhen a pencil is put into a beaker of water it looks ______. This is because the light is __________ as it leaves the water. The light travels _________ in air than water

slower reflected bent faster refracted

Choose three of these words to complete the sentences

Pencil trickWhen a pencil is put into a beaker of water it looks ______. This is because the light is __________ as it leaves the water. The light travels _________ in air than water

slower reflected bent faster refracted

Choose three of these words to complete the sentences

Air

Water

The Kingfisher• Refraction of light is the bending of light rays at the interface of dissimilar substances

Refraction

Air – lower refractive index

Water – higher refractive index

The Kingfisher•When light is passing from a higher refractive substance into a lower refractive substance the light rays bend away from the perpendicular to the surface.

perpendicular

Refraction

Air – lower refractive index

Water – higher refractive index

The Fish•When light is passing from a lower refractive substance into a higher refractive substance the light rays bend toward the perpendicular to the surface.

perpendicular

Refraction

Air – lower refractive index

Glass – higher refractive index

Glass Window

Air – lower refractive index

Refraction

•Light passing through a transparent material exits at the same angle it enters

RefractionAs the light ray enters the glass block it bends. This is called refraction. The light ray refracts towards the normal as it enters the block and away from the normal as it leaves the glass block. The light is refracted because it travels slower in the glass block than air.

Lens

ApplicationRefraction

Lenses

Refraction

•Refraction of light is the bending of light rays at the interface of dissimilar substances

•When light is passing from a higher refractive substance into a lower refractive substance the light rays bend away from the perpendicular to the surface.

•When light is passing from a lower refractive substance into a higher refractive substance the light rays bend towards the perpendicular to the surface.

•The angle at which the light is bent depends on the Refractive Indices of the two substances

Refraction•Who to - Key Stage 3

•Objective – Light behaviour in different transparent materials. Concept of refraction. How it behaves in different materials. Interpretation of everyday experiences.

•What they know – Light reflection, opacity, transparency, basic lenses.

•Format – 10 min presentation as introduction to subject with class discussions.

•Skills – Problem solving, experimental controls, observation, interpretation, application.

•What next – Practical investigation with different materials. Calculation of angles of deflection and Refractive Indices