Light Energy and Shadows
Light Energy
Enables us to see
Travels in straight lines
Form of energy
Sources of Light
Any object that gives off light on its own
Types of Light Sources
Stars
Sun
Some animals like fireflies
Burning fuels
Firewood
Lit Candle
Coals
Non-living things
Lamps
Torchlights
Electric bulbs
How Light Energy helps us to see
We can see objects in our surroundings
When light enters our eyes
Ways light enters our eyes
Object is
a source of light
reflects light from source of light that enters our eyes
Gives off light that enters our eyes
We can see the object directly
We are able to see them
Reflection of Light
Helps us to see images of objects
In the mirror
Light from surroundings
Reflected by the objects
Onto smooth surface of mirror
into our eyes
Through a periscope with mirrors
We are unable to see items at the other end of the periscope
When mirrors are arranged in a certain way in the periscope
They reflect light from the object into our eyes
Enabling us to see them
How Light Energy passes through different materials
Not all materials allow light to pass through them
Main groups of materials
Translucent
Opaque
Transparent
Allows most light to pass through it
Able to see through it clearly
Allows some light to pass through it
Unable to see through it clearly
Blurry/fuzzy image on the other side
Does not allow any light to pass through it
Unable to see through it at all
Types
Cloth
Some types of plastic
Tracing Paper
Frosted Glass
Types
Clean Air
Drinking Water
Clear Plastic
Glass
Types
Wood
Rubber
Metal
Clay
Measuring Amount of Light
A light sensor connected to a datalogger can be used to measure the amount of light that passes through an object
Experimental Set-ups
To find out the amount of light passing through an object with a light sensor and a datalogger
Experiment should be conducted in a dark place
Makes sure that there are no other light sources from surroundings are detected by light sensor
So accurate result can be produced
Thickness of Material
Thicker material
Less light that passes through
How Shadows Are Formed
When light is blocked by an object
A shadow is formed
A shadow always forms on the opposite side of the object
The shapes of the shadows are similar to the shapes of the objects
Materials/Objects
Translucent
Opaque
Transparent
Produce dark shadows
Produce light/blurry/fuzzy shadows
Produce no/very little shadows
When light is blocked by an opaque object with a hole in the middle
A bright patch
A dark shadow
Will form on the screen
Changing Shapes and Sizes of Shadows
When light is shining on different parts of the object
The object can produce shadows of different shapes
The positions of
Object(s)
Screen/Wall
Light source
Can affect the size of the shadow
When an object is
Further away from light source
Nearer to screen
A smaller shadow is formed
When a light source shines on an object from different angles/directions/positions
The length/size of the shadow will be different
Vertically above
Length/Size of shadow
Is the smallest/shortest
Angle of light source from object increases from vertically above
Length/Size of shadow
Is the longest/biggest
Daily Life
The Sun
shines on different objects
at different angles
at different times of the day
Sunrise
Mid-day
Sunset
Shadow is smallest/shortest
Shadow is longest/biggest
A bigger shadow is formed
Nearer to light source
Further away from screen