Download 11.4 Refraction of light

Refraction of light
Coin in Cup without water
Can’t see the Coin

This Phenomena is due to REFRACTION OR
BENDING of light
But doesn’t light travel in straight lines????

Well……yes……. and no……....

WHAT CAUSE LIGHT TO BEND?
Investigating Refraction
Useful words to describe refraction of light
angle of
incidence
air
glass
normal
angle of
refraction
Refraction Practical: Part A
LIGHT BOX
•
•
INCIDENT RAY 1
•
REFRACTED RAY 1
Acrylic plastic
block
Trace around the block
Join the crosses to
show the path of light
Join the point of entry
and exit from the block
to show the ray that
passes through the
block
INCIDENT RAY 2
REFRACTED RAY 2
Results
•
•
Draw in the normal to
the block at the point
of entry and exist of
the ray
Measure the angle of
incidence and angle for
refraction at the
interface between air
and plastic and then
plastic and air
PART B REFRACTION OF LIGHT IN
BICONCAVE AND BICONVES
FOCAL POINT
PRISMS
VIRTUAL FOCAL
POINT
Refraction
The path of light

When light travels within one medium its
speed is constant and it travels in a
STRAIGHT LINE
HOWEVER


When light moves between media of different
DENSITIES its speed changes and its
wavelength changes
If light enters the new media at an
angle(other than 90º) the ray of light will be
bent as it passes into the new medium.
Analogy:
Roller Skating or Marching Soldiers
Passing from faster to slower surface
 Bending is toward the normal

Similarly when a light wave enters a new
medium the part of the wave front hitting
the new medium first changes speed
before the next part of the wave front
 This causes the light to bend

Why is light refracted?




Click on the button below:
Experiment with different media and different
angles
Try an angle of incidence of 0º(light hitting
head on)
Refractive index is simply a measure of the
speed of light in a medium. The larger the
refractive index the denser the medium and
the slower light will move through the it.
Substance
State
Refractive
Index
Air
Gas
1.000293
Ice
Solid
1.31
Water
Liquid
1.33
Ethyl Alcohol
Liquid
1.36
Fluorite
Solid
1.43
Quartz
Solid
1.54
Salt
Solid
1.54
Tourmaline
Solid
1.62
Garnet
1.73-1.89
Cubic Zirconia
Solid
2.14 - 2.20
Diamond
Solid
2.41
Which is denser air or glass?
 What will happen to the speed of light as
it passes from air into glass?
 With respect to the normal, in what
direction will this make the light bend?

air
glass
So: from a less dense to a denser medium
• e.g. from air to glass
normal
air
glass
Original
path
• Light is bent towards the normal.
Which is denser water or air?
 What will happen to the speed of light as
it passes from water into air?
 With respect to the normal, in what
direction will this make the light bend?

water
air
From a denser to a less dense medium
• e.g. from water to air
normal
water
air Original
path
• Light is bent away from the normal.
Refraction
Examples of refraction of light
a) Bent chopstick
• The chopstick appears bent because
of refraction
Examples of refraction of light
b) Shallower in water
• The depth that the object is actually at
is called the real depth.
I
O
real
depth
Q1 A boy shines a torch under…
A boy shines a torch under water as shown.
Which one shows the correct path of the light
ray?
A
B
Path X.
Path Y.
C
Path Z.
D
All of them.
Q2 True or false: Light slows…
True or false: Light slows down when it enters
a material from air.
(T/F)
Q3 True or false: If light travel…
True or false: If light travel at the same speed
in all materials, refraction would still occur
when it passes from air to water.
(T/F)
Q4 True or false: When light is…
True or false: When light is incident on a
surface along the normal, only refraction
occurs; there is no reflection.
(T/F)
John says,
‘When hunting a fish under water, you
should aim your spear directly at the
fish.’
Do you agree?
Yes, of course.

No, because the fish is actually located
somewhere else.
No, because size of objects changes when
they are put under water.
Q5
Sketch a ray diagram for the...
Sketch a ray diagram for the fish to show it’s
apparent image in the water, as seen by the
fisherman.