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Chapter 17Reflection & Refraction
Reflection•When light rays
bounce back off of a medium boundary
Refraction•The bending of light
rays when passing from one medium to
another
Ray•A straight line path
representing the direction of a light
wave
Regular Reflection•Reflection off of a
smooth surface which results in reflected wave
that are parallel
Regular Reflection•Produce good images
•Mirrors give regular reflections
Diffuse Reflection•Reflection off of a rough
surface which results in reflected waves that are
not parallel
Diffuse Reflection•Because light waves are
scattered all over the place, no image can be
seen
Law of Reflection•The angle of
reflection equals the angle of
incident
Law of Reflection
= Normal
Optical Density•How fast light passes through a substance as compared to the speed of light in a vacuum.
Optical Density•As optical density increases, the speed in which light passes decreases
Index of Refraction (n)
•Ratio of the speed of light in a vacuum to the speed of light in a material
Indices of Refraction•Vacuum: n = 1.00•Air: n = 1.0003•Water: n = 1.33•Ethanol: n = 1.36
Indices of Refraction•Crown glass: n = 1.52•Quartz: n = 1.54•Flint glass: n = 1.61•Diamond: n = 2.42
Speed of Light in Other Substances
c
vsubnsub =
Speed of Light in Other Substances
c
nsubvsub =
Solve for the speed of light in each of the
following:water (n = 1.33)
crown glass (n = 1.52)diamond (n = 2.42)
Solve for the speed of light in a
substance with an optical density of
1.50:
Snell’s Law•The ratio of the sine of the angle of incidence over the sine of the angle of refraction is constant for any substance
Snell’s Law
sin i
sin r
n =
Snell’s Law
ni sin i = nr sin r
Snell’s Law
n1 = air n2 = water
i
r
Draw a model with a light ray passing from one medium to another more optically dense
medium. Include reflection & refraction
A light ray from air(nair = 1.00) & strikes
glass (nglass = 1.52) with an incident angle of 30.0o. Calculate the angle of refraction:
A light ray from air(nair = 1.00) strikes glass
(nglass = 1.61) with an incident angle of 36.9o. Calculate the angle of
refraction:
A light ray from air(nair = 1.00) & strikes
diamond (ndiamd = 2.42) with an incident angle of 45.0o. Calculate the angle of refraction:
A light ray incident from air (nair = 1.00) at
45.0o passes into an unknown substance at
30.0o. Calculate its index of refraction:
Total Internal Reflection
• When light passes from a more optically dense
substance to a less optically dense one, the angle of refraction > the angle of
incident
Total Internal Reflection (TIR)•When the angle of
refraction 90o, total internal reflection
occurs.
Calculate the angles where TIR occurs when light passes
from the following to air:water (n = 1.33)
crown glass (n = 1.52)diamond (n = 2.42)
Applications & Effects• Prisms• Fiber Optics• Mirages• Red Sunsets• Rainbows
Prisms• When light pass through a
prism the various wavelengths of light are dispersed or separated into a spectrum
Prisms
Fiber Optics• A light wave can pass through a thin glass thread surrounded by a reflective substance. Even if the
glass thread is bent, the wave passes through as it reflects off
the sides.
Mirages•Light refracted from a far away source looks closer
Mirages
Sunsets & Rises• Sunlight is refracted as it
strikes the atmosphere at great angles bending light towards Earth
Sunsets• Because different
wavelengths are refracted differently, colors change
Sunsets
Rainbows• Sunlight is refracted &
reflected by rain droplets dispersing the light into a spectrum
Rainbows
Rainbows
Rainbows fallfrom 40 – 42o
from incident
Rainbows
Rainbows fallfrom 40 – 42o
from incident
A light ray from water(nw = 1.33) & strikes
diamond (ndiamd = 2.42) with an incident angle of 53.0o. Calculate the angle of refraction:
Answer the questions at the
end of Chapter 16
Answer the questions at the
end of Chapter 17
A light ray from water(nw = 1.33) & strikes
glass (nglass = 1.51) with an incident angle of 53.0o. Calculate the angle of refraction:
Calculate the angle of total internal
reflection of pukon with n = 3.00
An incident ray from air strikes quartz (n = 1.50) at an angle of 30o from normal.
Calculate: refl & refr