Download Properties of Light

Light
1)
2)
3)
4)
Properties of light
Reflection
Colors
Refraction
Part 1 – Properties of Light
Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.
We see things because they
reflect light into our eyes:
Homework
Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects
Reflectors
Shadows
Shadows are places where light is “blocked”:
Rays of light
Properties of Light summary
1) Light travels in straight lines
2) Light travels much faster than sound
3) We see things because they reflect light
into our eyes
4) Shadows are formed when light is blocked
by an object
Part 2 - Reflection
Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!
Image - is a position in space where all the
reflected light appears to diverge from.
Images formed by plane
mirrors are virtual
1.The image formed by a plane mirror is
Virtual Image
– not real therefore can not be caught on
a screen
– Images are formed in locations where
light does not actually reach
– Rays do not actually cross at the point
behind the mirror.
• They only appear to have originated there.
2.The object distance (often represented by
the symbol do) is equal to the image
distance (often represented by the symbol
di).
3.Dimensions of the image are the same as
the dimensions of the object .
4. The image is upright
5. Left right reversal – The image is laterally
reversed.
Specular vs. Diffuse Reflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
Reflection off of smooth surfaces
such as mirrors or a calm body of
water leads to a type of reflection
known as specular reflection.
Reflection off of rough surfaces
such as clothing, paper, and the
asphalt roadway leads to a type of
reflection known as diffuse
reflection.
Color
White light is not a single color; it is made up
of a mixture of the seven colors of the
rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split up”
by raindrops.
The colors of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Adding colors
White light can be split up to make separate colors.
These colours can be added together again.
The primary colors of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding red
and green
makes yellow
Adding blue and
green makes cyan
(light blue)
Adding all
three makes
white again
Seeing color
The color an object appears depends on the colors of
light it reflects.
For example, a red book only reflects red light:
White
light
Only red light
is reflected
A pair of purple trousers would reflect purple light
(and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light
Using colored light
If we look at a colored object in colored light
we see something different. For example,
consider a football kit:
Shirt looks red
White
light
Shorts look blue
In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
Refraction is the bending of light
when the light passes from one medium to
another.
air
glass
Useful words to describe refraction of light
angle of
incidence
air
glass
normal
angle of
refraction
Examples of refraction of
light
Bent chopstick
• The chopstick appears bent because of
refraction
The bending occurs because the speed in
which light travels through a substance
depends on the substance's density. In
air light travels at about 186,000 miles
per second but in water light travels only
about 140,000 miles per second (see
chart below). Since light travels slower in
water than in air, water is said to have a
greater optical density than air.
‘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.
“The Inverse Square Law”
The Energy we receive is
inversely proportional to the
square of the distance.
Diffraction
Diffraction is the apparent bending of waves
around small obstacles and the spreading
out of waves past small openings.
POLARIZATION
Only
transvers
e waves
may
become
polarized.
•Sun glasses reduce the glare of
bright light using the phenomenon
of polarization