Today we are learning ?
• what is light ?
• How does light travel ?
• Porperties of light
• Transparent and opaque objects
• What is a shadow ?
• Properties of shadow
• Importance of shadow
What is light made of?
• This is not an easy question. Light has no mass
and is not really considered matter.
• So does it even exist? Of course it does!
• We couldn't live without light. Today scientists
say light is a form of energy made of photons.
Light is unique in that it behaves like both a
particle and a wave.
what is light ?
• You may see the light from the sun , natural
source of light. Light is a form of energy
• We are to see light from candle, bulb, tube
light (artificial sources of light)
We can see light when :
• An object gives off its own light (like a sun)
• An object reflects light into our eyes
• Objects that give off light are called sources of
• A source of LIGHT make light. THE SUN and
other stars, fires, torches, and lamps all make
their own light and so are examples of
SOURCES OF LIGHT
• Some animal, such as FIREFLIES and GLOW-
WORMS, are light sources. They make their
own light to attract mates.
Fill in the gaps using the words :
source – straight – starts - universe
• Something that produces its own light is
known as a ............ Of light.
• Fire, lamps and ......are all examples.
• Light travels is ....... Lines and is the
fastest thing in the .......
Why does light go through some
things and not others?
• Depending on the type of matter it comes into contact
with, light will behave differently.
• Sometimes light will pass directly through the matter,
like with air or water.
• This type of matter is called transparent.
• Other objects completely reflect light, like an animal or
a book. These objects are called opaque.
• A third type of object does some of both and tends to
scatter the light. These objects are called translucent
What are the Properties of Light?
• Following are the important properties of light
• Light travels in a straight line.
• The speed of light is faster than sound. Light
travels at a speed of 3 x 108 m/s.
Can we see through ALL objects ?
• WE can see lights can pass though GLASS
BUT WHAT ABOUT THIS ?
• WELL we cannot see clearly frosted glass.
• Because light is partially blocked
How does light travel ?
• Light travel in the street line in the air
• This line are called rays
• Light travel in wave
• Light moves at the fastest known speed in the universe.
Nothing moves faster than (or even close to) the speed of light.
In a vacuum, where there is nothing to slow it down, light travels 186,282 miles per
Wow, that's fast! When light travels through matter, like air or water, it slows down
some, but it's still pretty fast.
To give you an idea as to how fast light is, we'll give you some examples.
The Sun is almost 93 million miles from the Earth. It takes around 8 minutes for light to
get from the Sun to the Earth. It takes around 1.3 seconds for light to go from the
moon to the Earth.
What is Reflection
• Reflection (when light from an object is
reflected by a surface, it changes direction. It
bounces off surface at the same angle as it
hits it. Smooth, shiny surface such a mirror
and polished metals reflect light well. Dull and
dark surfaces such as dark fabrics do not
reflect light well
When light hits an object, its transmitted,
absorbed, and/or reflected
The light on the left is reflected, the light in the middle is absorbed and
the light on the right is transmitted. Any object you can see must at least
partially reflect light to your eyes. Objects can ALSO absorb and/or
1. Transmitted – light that passes through a substance
a.Transparent – visible light is transmitted easily and objects are
b.Translucent – some visible light is transmitted, but some is
scattered (or diffused) so that objects are not clearly seen
Law of Reflection
"Normal" is the imaginary line that is perpendicular to the object. Whether a
surface is smooth or bumpy, light ALWAYS obeys the Law of Reflection
The blue incident light rays scatter in different directions (red rays) off a
rough surface, but STILL obey the Law of Reflection
Absorbed – light energy hitting the
surface is converted to heat energy
a. Dark or black objects absorb more
light and feel hotter than lighter or
b. Objects that do not transmit or
reflect much visible light, absorb it, so
the object appears opaque (you can't
see through it)
How Light Reflects
• When light reflects off a
surface, the angle of
incidence (incoming light) is
equal to the angle of
reflection (outgoing light) –
called “Law of Reflection”
• i. If you shine a narrow
beam at a highly polished
surface (like a mirror), you get
a narrow beam of light
reflected back off it (called
• ii. If you shine a narrow
beam of light at a rough
surface, the light scatters in
all directions, (called diffuse
reflection) but still obeys Law
Compare light that reflects off a
smooth and rough surface
When light reflects off a surface, it obeys the Law of Reflection (the
angle of incidence is equal to the angle of reflection), whether or not
the surface is smooth. The light is reflecting off the flower to the
water and then back to your eye.
Compare light that reflects off a
smooth and rough surface
In the wavy water, the some of the
light is scattered so you do not see a
perfect reflection. If the water was
even more disturbed - for example,
stormy and very wavy - you might
not see the reflection at all because
the light is even more scattered so
that it does not reach your eyes.
When light hits something and
bounces off it we say it reflects
Light is what helps
us to see we
objects only when
light reflects off
them when its
dark and no light
is reflecting we
• A mirror is very shiny
thats why its reflects so
much light and we see
ourselves in it materials
that are dull do not
reflect a lot of light
• When light travels through water , glass,
plastic or any other thick substance it slow
1. A pieceof plastic wrap
2. A piece of waxed paper
3. A piece of aluminium foil..
Let us now see what our TRANSPARENT, TRANSLUCENT, and,
OPAQUE Objects we can observe objects to find out how much light
passes through them.
A piece of plastic wrap, a piece of waxed paper, a piece of
If you held them up to the light to how much light shone through
1. So the light would pass directly through the plastic wrap light
passes easily through clear objects like glass and clear plastic we
call these objects TRANSPARENT
2. The light would somewhat shine through the wax paper but not
completely. Few objects like stained glass windows and thinly
colored plastic let SOME LIGHT THROUGH, but not all. They are
3. The light in the aluminium foil , no light passes. We call objects
that BLOCK ALL LIGHT OPAQUE
• When light hits an opaque object it is stopped in its tracks it cannot pass behind the object
that blocks the light you will see a SHADOW
What is a shadow ?
• How are shadows formed ?
• A shadow is formed when an OBJECT BLOCKS
Size of SHADOWS
• It changes with the distance between
the object and the light source:
• If we move the light CLOSER to the
object, the shadow is BIGGER
CAN YOU SEE IT ?
• If we move the light FURTHER from the object
, the shadow is SMALLER
Light helps us to survive
• Without sunlight our world would be a dead dark place.
• Sunlight does more than just help us see (which is pretty
• Sunlight keeps the Earth warm, so it's not just a frozen ball
in outer space.
• It also is a major component in photosynthesis which is
how most of the plant life on Earth grows and gets
• Sunlight is a source of energy as well as a source of vitamin
D for humans.