Refraction

D. Crowley, 2008

Refraction

• To be able to apply your knowledge of refraction to explain new situations

Refraction

• Light travels in straight lines

• Refraction is caused because light can speed up / slow down (and hence bend) depending on the medium it travels through

• The light ray bends towards the normal as it enters

• The light ray bends away from the normal as it leaves

• The ray entering the block is parallel to the ray leaving the block, if the block has parallel faces

• A ray entering the block at 90° is not refracted

Refraction

Water

• Try for yourselves the penny in the beaker trick…

• Water is denser than air, so light is refracted when it travels through the surface of the water

• This is why sticks seem to be bent if they are partly underwater, and why swimming pools look shallower than they really are

• Refraction lets you see objects that are normally hidden…

Archer Fish

• The Archer fish is a predator that shoots jets of water at insects near the surface of the water, e.g. on a leaf

• The Archer fish allows for the refraction of light at the surface of the water when aiming at the prey

image of prey

prey location

• The fish does not aim at the refracted image it sees, but at a location where it knows the prey to be

Pencil

• Your assessed task is to look at the pencil in the water, and explain why this is happening

• You will be assessed on: -– Your knowledge and understanding of light (and how it travels)– Your ability to explain ideas clearly

Leveling

• Level 4 - understanding that light travels in straight lines, but that the water causes it to bend (refract)

• Level 5 - explanation that refraction occurs when the light changes speed

• Level 6 - understanding that refraction occurs when the light slows down as it hits a more dense medium, and speeds up again when it enters a less dense medium (i.e. slow in water; faster again in air)

• Level 7 - explanation that the direction of the light will bend in different circumstances

Trick Questions

Trick Questions