LIGHT
REFLECTION AND REFRACTION
What do you know about light?
Light as a wave: electromagnetic wave
When the electrically charged particle vibrates, it moves back and forth a little. This movement
makes the electric field surrounding it vibrate, too.
The vibration of the electric field creates a magnetic field.
The vibration of an electric field and a magnetic field together produces an EM wave
Light as a particle : photon
The photon is sometimes referred to as a "quantum" of
electromagnetic energy.
Light is a Form of Energy
■ ‘the’ source of energy for plants
■ Indirect source of energy for animals
Light Energy
Conversion of Light Energy
Light  kinetic energy
Crookes Radiometer
Light  Electrical Energy
Transmission of Light
■ Light travels in straight lines
Grand Central Station, New York
To Show That Light Travels in Straight Lines
cardboard
light
bulb
thread/string
Shadow
To Show the Formation of Shadows
White Sheet/Cardboard
Object
Torch
This also shows that
light travels in straight
lines.
How Does Light Travel?
■ Light traveling in a vacuum is faster than anything else scientists have discovered.
■ In space, which is almost a vacuum, light travels at 300,000 km/s.
■ Light travels slightly slower in air, glass, water, and other materials.
Light travels about 880,000 times faster
than sound. You can observe this fact by
watching and listening to a
thunderstorm.
Thunder and lightning are both produced
at the same time
■ Light takes
about 8.3
min to
travel from
the sun to
the Earth.
■ Earth is
150 million
km from
the sun.
Reflection
■ Reflection happens when light
bounces off an object.
■ Light reflects off objects all
around you.
■ You see the objects because the
reflected light travels to your
eyes.
The law of reflection
■ The angle of incidence of light is equal to the angle of reflection.
Reflection
• Practically all surfaces reflect light
– Shiny smooth surfaces have regular reflection
– Matt (dull) surfaces have scattered reflection
Refraction
■ Refraction happens when a wave bends as it passes from one
material into another.
■ Light travels at different speeds through different materials.