Refraction of light

1 John says, ‘When hunting a fish under water, you should aim your spear directly at the fish.’ Do you agree? Yes, of course. No, because the fish is actually located somewhere else.  No, because size of objects changes when they are put under water.

2 When sunlight falls on the water surface, which of the following occur(s)?  It is reflected back to the air.  It refracts into the water.  It is absorbed by water and turned into heat.

Introduction Refraction is the bending of light when the light passes from one medium to another. air glass

Introduction Useful words to describe refraction of light angle of incidence incident ray normal air glass refracted ray angle of refraction

Introduction From a less dense to a denser medium e.g. from air to glass normal incident ray air glass refracted ray Light is bent towards the normal.

Introduction From a denser to a less dense medium normal incident ray e.g. from water to air air water normal incident ray refracted ray Light is bent away from the normal.

Laws of refraction The incident ray, the refracted ray, and the normal all lie in the same plane. incident ray normal normal air air glass glass refracted ray refracted ray

Example 3 nw sin w= na sin a Applying Snell’s law,  1.33  sin w = 1  sin 30  sin w = sin 30/1.33 = 0.376 air water 30  w = 22.1 22.1

Q1 A boy shines a torch under… A boy shines a torch under water as shown. Which one shows the correct path of the light ray? A Path X. B Path Y. C Path Z. D All of them.

Q4 True or false: When light is… True or false: When light is incident on a surface along the normal, only refraction occurs; there is no reflection. (T/F)

1st statement 2nd statement Q5 Statements:... 1st statement 2nd statement Light is bent towards the normal when it passes from air to glass. Glass has a greater refractive index than air. true? true? Yes Yes

4 Examples of refraction of light a Bent chopstick The chopstick appears bent because of refraction

4 Examples of refraction of light b Shallower in water O I real depth The depth that the object is actually at is called the real depth. Simulation

4 Examples of refraction of light c Flickering objects in hot air The object you see through the unstable hot air appears blurred and flickering.

Q1 True or false: Light slows… True or false: Light slows down when it enters a material from air. (T/F)

Q2 True or false: The refractive… True or false: The refractive index cannot be smaller than 1. (T/F)

Q3 True or false: If light travel… True or false: If light travel at the same speed in all materials, refraction would still occur when it passes from air to water. (T/F)

Q4 True or false: If the speed of… True or false: If the speed of light in raindrop is equal to that in air, there would be no rainbows. (T/F)