What is Refraction? • The bending of light as it travels from one medium to another.
Examples of Refraction • A spoon appears bent as it enters water. • Attempting to touch an object under water and missing it.
Examples of Refraction • Seeing an object just under the surface of water in a dish, when you could not see it without the water (Bill Nye!)
What Causes Refraction? • The speed of light is different in different mediums. • You see things because of the light rays reflecting from them • As rays pass through a boundary, the light rays speed up or slow down causing them to bend
Analogy….. • Wagons travelling from a paved road to sand.
Explanation….. • As the right front wheel hits the sand, the wagon changes direction because the wheel in the sand turns slower.
Refraction Fast Medium Slow Medium
Relative Speeds of Light Faster Slower • Vacuum • Air • Water • Acrylic (clear plastic)
The thicker the medium, the slower the light goes • Thickness is known as optical density (reflected in the index of refraction value)
refracted ray angle ofrefraction angle ofincidence incident ray Refraction Light Rays
Rules for Refraction • The incidentray and the refracted ray are on opposite sides of the line that separates the two media.
Rules for Refraction • Light bends towards or away from the normal depending on the speed of light in the second medium.
Rules for Refraction • Light bends toward the normal if it travels more slowly in the second medium than in the first.
Faster to slower medium • Bends towards the normal • Slower to faster medium • Bends away from the normal
Rules for Refraction • Light bends away from the normal if it travels faster in the secondmediumthan in the first.
Partial Reflection • Reflection and refraction often happen together. • Light hitting the water reflects off the water, but also refracts as it enters the water illuminating objects below the water.
Examples of Partial Reflection • Glass may have special film to allow light in, but reflect incident light as well.(mirrored buildings) • Mirrored surfaces you can see through, but others cannot! (sunglasses)
Vocabulary! Refraction Angle of Refraction
Homework! Pg. 519 #2 – 5