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11.1Refraction of Light
LEARNING GOALS§ I will be able to describe what refraction is§ I will be able to state and use the rules of refraction§ I will learn key words: refraction, refracted ray, angle of refraction, index of refraction, dispersion
https://www.youtube.com/watch?v=jQDRNb-E-cY
Refraction§ light travels in a straight line and at a constant speed in the same medium
§ when light travels from one medium to another (e.g. from air to water), light rays refract (bend) and both the direction and speed change
Refraction§ the bending of light as it travels, at an angle, from a material with one refractive index to a material with a different refractive index
Marching Band AnalogyWhy does light refract?
§ when one end of the band slows down, the direction of travel of the entire band changes
Imagine…
A beam of light was made up of people walking in formation…..like
a marching band!!
Imagine…Light traveling in air is like the
marching band walking on grass.
Light traveling in glass is like the marching band walking in mud
Air Glass
Air Glass
Entering a more dense medium causes the light beam to slow down
Air Glass
Beam of light moving towards an air-‐glass interface
Air Glass
The parts of the light that hit the air-‐glass interface first slow down and first causing the line to bend.
Air Glass
The beam of light is now travelling in a different direction
What happens if the light travels from a more dense medium to a less dense medium (i.e. glass to
air)?
What happens if the marching band walks from mud to grass?
OR
Air Glass
A beam of light travels towards a glass-‐air interface
Air Glass
The parts of the light that hit the air-‐glass interface first speed up and first causing the line to bend.
Air Glass
The beam is now travelling in a different direction.
Refraction and Raysrefracted ray§ the ray that is bent upon entering a second mediumangle of refraction (R)§ the angle between the normal and a refracted ray
Direction of the Refracted Ray§ when a light ray travels from a medium in which its speed
is faster (air) to a medium in which its speed is slower (water) the refracted ray bends toward the normal
fast to slow – towards the normal
Direction of the Refracted Ray§ when a light ray travels from a medium in which its speed
is slower to a medium in which its speed is faster, the refracted ray bends away from the normal
slow to fast – away from the normalArcher Fish Video
Dispersion§ the process of separating colours by refraction
§ white light (all wavelengths of visible light) refracts twice:1. when it enters the prism2. when it leaves the prism (separates into a spectrum of colours)
Dispersion§ each colour of light travels at a slightly different speed§ only in a vacuum (space with no matter) do all colours travel at
the same speed: 3.00 x 108 m/s§ e.g. blue light bends more than red light (blue light travels
slower than red light)
Roy G. Biv
How much of the light refracts?
§ speed of light in a vacuum is
§ the speed of light in any other medium is less than that e.g. the speed of light in water is 2.26 x 108 m/s
3.00 x 108 m/s
Index of Refraction§ the ratio of the speed of light in a vacuum to the speed
of light in a given medium
Disappearing Glass Video
Index of Refraction
§ the index of refraction is always greater than 1§ as the speed of light decreases due to the medium, the index
of refraction increases
Sample ProblemCalculate the speed of light in fused quartz. The index of refraction for fused quartz is 1.46.
Equationn = c
v
n = index of refractionc = speed of light in a vacuumv = speed of light in a medium
Rearrange the equation!!!
Givenn = 1.46c = 3.00 x 108 m/sv = ?
v = c n
v = 3.00 x 108 m/s 1.46
v = 2.05 x 108 m/s The speed of light in fused quartz is 2.05 x 108 m/s
c
vn
If the speed of light in water is 2.26 x 108 m/s, calculate the index of refraction for water.
Equationn = c
v
n = index of refractionc = speed of light in a vacuumv = speed of light in a medium
Givenn = ?c = 3.00 x 108 m/sv = 2.26 x 108 m/sn = 3.00 x 108 m/s
2.26 x 108 m/sn = 1.33 The index of refraction for
water is 1.33.
https://www.youtube.com/watch?v=f8oV4RBYR9U
Refraction and Fish?!?!?!?!
Homework§ Read p. 449-455 in the textbook.§ Complete “Section 11.1 Review” Worksheet