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Refraction
Level : Physics I Teacher : Kim
Review in Refraction of Light
incident ray θi
AIR
Normal line
WATER or
GLASS (^) θr refracted ray
When the light ray goes into a denser medium(ex. air to water or air to glass), the rays bend toward the normal line. So the incident angle θi is greater than the refracted angle θr. => θi > θr
When the light ray goes into a less dense medium(ex. water to air or glass to air), the rays bend away from the normal line. So the incident angle θi is less than the refracted angle θr. => θi < θr
Index of Refraction ‘Can we slow down the speed of light?’ When light enters a new medium its speed changes depending on the density of the new medium. The ratio of between the speed of light in vacuum and speed of light in the new medium can be expressed as
Index of refraction of a medium(n) = Speed of light in a vacuum (c) Speed of light in the medium(v)
=> n = 𝒄 𝒗
where c =3 108 m/s
The index of refraction(n) for vacuum is set as ‘ 1 ’. So the index of refraction for any materials will be greater than ‘1’. Hence, index of refraction(n) cannot be lower than ‘1’.
AIR
Normal Line
θr refracted ray
WATER or GLASS incident ray θi
Q1) Light has a speed of 1.8 108 m/s in particular glass. Calculate the index of refraction
for this glass. (speed of light in a vacuum c= 3 108 m/ s )
(a) 1.23 (b) 1.67 (c) 1.81 (d) 2.
Q2) The index of refraction for a sample of water is 1.33. How fast does light travel
through this water? (speed of light in a vacuum c= 3 108 m/ s )
(a) 8.24 107 m/s (b) 1.09 108 m/s (c) 2.26 108 m/s (d) 4.01 108 m/s
**** Snell’s Law** important!
- When light passes at an angle from a medium with a lower index of refraction to one with a higher index of refraction, it will bend towards the normal line
- When light passes at an angle from a medium with a higher index of refraction to one with a lower index of refraction, it will bend away the normal line
- The extent to which a wave of light bends when it passes at an angle into a new medium, it given by Snell’s Law
n 1 sin 1 = n 2 sin 2
where 1 is the angle of incident and 2 is the angle of refraction
Q 3 ) Light passes through air( n 1 =1.00) and strikes the surface of a piece of glass at an angle of 58º from the normal. The angle of refraction is 33º measured from the normal. Calculate the index of refraction for the glass. a) 1.32 b) 1.56 c) 1.73 d) 1.
θi=58° air θr =33º
glass
Press 2nd SIN type in 0.5 ) press ‘enter’
n 1 sin 1 = n 2 sin 2
where 1 is the angle of incident and 2 is the angle of refraction
Q5) A searchlight on a yacht is being used at night to illuminate a sunken chest.
At what angle of incidence 1 should the
light be aimed at? a) 35º b) 4 4º c) 52º d) 67º
θ 1 air n 1 =1. water n 2 =1. θ 2 3.3m
Chest
2.0m
