Refraction

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Angle of Incidence

Angle of Refraction

60°  

50°  

40°  

30°  

20°  

10°  

0°  

Discuss1. When light travels from air into acrylic, as

the angle of incidence gets smaller, the angle of refraction: 

a)gets greater b)becomes equalc) gets smaller

 2. When light travels from air into acrylic with

an angle of incidence of 0º (along the normal), what happens to it?

3. When light travels from air to water at an

angle of incidence greater than 0º, it is bent

______________________ the normal.

The Reappearing Coin

How can we see a coin that is not in our line of sight?

Refraction

Refraction is the bending of light as it moves from one medium to another

All transparent materials (e.g., glass, plastic, water, diamond, etc.) refract light

These materials are said to be optically dense

What causes refraction?

Light refracts because light travels at different speeds in different mediaMedium Speed

Air (vacuum) 3.00 x 108 m/sWater 2.26 x 108 m/sAcrylic 1.76 x 108 m/s

Refraction Terminology

The incident ray, refracted ray, and the normal all lie in the same plane

The incident ray and the refracted ray are on opposite sides of the line that separates the two media

Refraction Terminology

The incident ray is the ray which meets the different medium at the “point of incidence”

The refracted ray is the ray which has bent into the new medium

The angle of incidence (i) is the angle between the incident ray and the normal

The angle of refraction (R) is the angle between the refracted ray and the normal

Your turn

Activity – Refraction from Air to Acrylic

Rules for Refraction

1. When travelling from a “fast” medium to a “slow” medium, light bends towards the normal

Car Analogy

When the car leaves the pavement and enters the muddy surface, the tires move more slowly than they did on the pavement, causing the car to bend towards the dashed line in the diagram (normal)

Rules for Refraction

2. When travelling from a “slow” medium to a “fast” medium, light bends away from the normal

Car Analogy

When the car enters the smooth pavement, the tires move more quickly than they did on the muddy surface, causing the car to bend away the dashed line in the diagram (normal)

The Broken Straw

Why does the straw appear in two pieces at the waters’ surface?

The Broken Straw

Light coming from the part of the straw below the surface of the water is traveling from water (more dense) to air (less dense)

The speed of light is faster in air than in water, so light will bend away from the normal

The human brain perceives light to travel in straight lines, so it appears to us as if the light source is behind the straw

Your turn

Refraction Practice