refraction d. crowley, 2008. refraction to be able to apply your knowledge of refraction to explain...
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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
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