Refraction of light

1John 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.

2When 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.

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

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

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

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

 sin i is directly proportional to sin r. sin i sin r O Relation between angle of incidence and angle of refraction i = angle of incidence r = angle of refraction straight line passing through the origin

Laws of refraction VideoSimulation

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

i.e. sin i sin r = constant The ratio of the sin i to sin r is constant. – This is called Snell’s law. Laws of refraction In general, n 1 sin  1 = n 2 sin  2

sin i sin r refractive index n = sin  a sin  g ang=ang= a: air g: glass e.g. for glass, where Refractive index

MaterialRefractive index Glass1.5 – 1.7 Water1.33 Perspex1.5 Diamond2.42 Refractive indices of some materials Refractive index

Refractive index and speed of light distance that light travel in 1 s vacuum (or air) 3  10 8 m water (n = 1.33) 2.25  10 8 m glass (n = 1.5) 2  10 8 m diamond (n = 2.42) 1.25  10 8 m diamond (n = 2.42) 1.25  10 8 m

3Refractive index and speed of light distance that light travel in 1 s vacuum (or air) 3  10 8 m water (n = 1.33) 2.25  10 8 m glass (n = 1.5) 2  10 8 m diamond (n = 2.42) 1.25  10 8 m diamond (n = 2.42) 1.25  10 8 m Refractive index Speed of light fastest slowest

air water Example 3 A ray of light passes from air into water. Angle of incidence = 30  What is angle of refraction in water? n water = 

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

Example 4 A ray of laser hits a rectangular block. The table gives a set of results. Notes:  a = angles of incidence,  g = angles of refraction. (a)Is the refracted ray bent towards or away from the normal? agag 15  30  45  60  75  11  18  28  34  40  Towards

Example 4 (b)Find out how sin  a and sin  g are related by plotting a graph of sin  a against sin  g. agag 15  30  45  60  75  11  18  28  34  40  sin  a sin  g

Example 4 sin  a sin  g sin  g sin  a  0.20 =  0.30 = 0.64 slope = =   0.20

Example 4 (c)Find the refractive index n g of the glass block in used in the experiment. Refractive index = = slope of graph sin  a sin  g = 1.52  The refractive index of the glass block used is 1.52.

Q1A boy shines a torch under… A boy shines a torch under water as shown. Which one shows the correct path of the light ray? APath X. BPath Y. CPath Z. DAll of them.

Q2A beam of light travels air to… A beam of light travels from air to water. Which of the following is equal to the ratio sin r : sin i ? An water : 1 Bn air : 1 C1 : n water D1 : n air water air normal i r

Q3A light rays is incident on a… A light ray is incident on a glass prism. Which equation can be used to find  ? 30  20  40   Dsin 40  = 1.5 sin  A = sin 30  sin 20  sin  sin 40  B = sin 30  sin 20  sin 40  sin  C = 1.5 sin  sin 40 

Q4True 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)

Q5Statements:... 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? Yes

4Examples of refraction of light aBent chopstick The chopstick appears bent because of refraction

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

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

Q1True or false: Light slows… True or false: Light slows down when it enters a material from air. (T/F)

Q2True or false: The refractive… True or false: The refractive index cannot be smaller than 1. (T/F)

Q3True 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)

Q4True 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)

Q5Sketch a ray diagram for the... Sketch a ray diagram for the tip of the chopstick to show why the chopstick looks bent when dipped into water.