Transcript 4.5 – Refraction of Light

p. 332 – 335
How does light move?
 light travels in the path that takes the least
amount of time
 in a single medium, that’s a straight line
 when there’s more than 1 medium that light is
travelling through, the path that takes the least
amount of time
is not a straight
line
What do we call light that bends?
refraction = the bending of light as it travels
through one (transparent or
translucent) medium to another
 due to a change
in speed that
light rays travel
 reflection still occurs, but we focus more on the
incident ray with refraction
 with mirrors the focus was on the reflected ray
refracted ray = ray that
bends when it
enters another
medium/ material
(from air to glass)
angle of refraction
(R) = angle
between the
normal and the
refracted ray
 all media (materials) allow for light to pass
through at different speeds
 ex: air allows light to travel fast, water slower, diamond
even slower
 light travels fastest in air
 at a speed of 3.00  108 m/s or 300 000 km/s… WOW!
 in any other medium, light slows down a little
 see p. 334 Fig. 4.35
How does light bend from a fast
medium to a slower one?
 if a light ray travels from air into another medium
(water, glass, etc.), light slows down and the
refracted ray bends toward the normal
 fast medium to slow medium  light bends toward the
normal
p. 335 Fig. 4.36
How about a slow medium to a
faster one?
 if a light ray travels from another medium (e.g.,
water) into air, light speeds up and the refracted
ray bends away from the normal
 slow medium to faster medium  light bends away from
the normal
p. 335 Fig. 4.36
Dispersion
 the process of separating colours by
refraction
 prisms do this
 blue band is at the bottom and is the thickest, so
it bends the most
Apparent depth
 An optical illusion that causes a person to perceive an




object is in a different position than where it really is
Caused by refraction
Our brains see light in straight
lines only
When light goes from air to water,
it bends (but our eyes think the
light travels straight)
This is why when you reach for a
coin in a fountain it isn’t where
you think it is
What other cool optical illusions
are a result of refraction?
 Mirages
 Shimmering
 Rainbows
 Sundogs
Mirages & Shimmering
 Mirages
 refraction of light rays reflecting off objects far away
 caused by uneven heating of air close to Earth’s surface
 image that forms is displaced
 Shimmering
 refraction of light rays close
to the ground on very hot
days
Rainbows
 Caused by reflection, refraction & dispersion of light
in droplets of water in air
 Water droplets act like tiny prisms, separating white
light
 This is why rainbows are only ever seen after it rains
How does a double rainbow form?
Sundogs (aka parhelia)
 Very similar to rainbows, but instead of water droplets
light rays refract in ice crystals high in the atmosphere
 Caused by the refraction of light in ice crystals
 Are found on very cold days in Northern climates