Geometric Optics
Light and Geometric Optics – Are you Ready? (25 minutes)
 Group
activity
 Answer questions on chart paper
 5-10 minutes students brainstorm and record ideas
 Groups will take turns in front of class explaining
their response
What is Light?
 Almost anything can give out light
 you can see some things because they give off
their own light . The Sun for example
 Sunlight is the energy that makes light possible
on Earth
 nuclear reactions occurring within the Sun
produce tremendous amounts of energy
 one form this energy takes is light, which the Sun
emits in all directions
 you see other things because daylight, or other light,
bounces off them
Some facts about Light
 light is a type of energy
This calculator doesn’t need a
battery to keep going. Just
plenty of sunlight
Light waves can travel through
empty space
• Other wise it wouldn’t be possible to see
the Sun and the stars. The waves travels
very fast – about 300 000 km every
second
Light travels in straight lines
The edge of a laser beam shows this
 you can see the path of the beam
because dust in the air glints when light
reflects from it
Light is made up of waves
throw a stone into a pond and ripples
spread across the surface of the water
 light travels in much the same way
 ”ripples”are tiny electric and magnetic
vibrations
And they don’t
need water to
travel accross
Rays and beams
 in diagrams, rays are lines with arrows on
them
 they show which way the light is going
 a beam is drawn using several rays side
by side
Holograms
 the picture on a credit card is called a hologram
 it looks three-dimensional Its colour changes as
you look from different angles
 image is actually a pattern of light waves
reflecting from surface of card
How is light produced?
 the Sun is luminous, meaning it produces
its own light
 a table does not produce its own light, so
its non-luminous
 a non-luminous source can be seen only
by using reflected light
Types of light
Light from incandescence
• when a stove is set to a high temperature,
the filament glows.
• the production
• Read pages 470 to 475 and make short
notes on types of light
Demonstration of source of light using
discharge tubes
• Explanation: light produced by electrical
discharge is caused by a current passing
through a gas in the discharge tube.
• the current provides energy to the electrons in
the atoms of the gas causing them to move up
energy levels (orbits)
• they release in the form of visible light when
they return to their original energy levels. Every
element gives off a particular colour
The Nature of Light
Light is the only form of energy that can travel like a
wave through empty space and through some
materials.
 Light behaves like a special kind of wave, called
an electromagnetic wave'
 In water waves, the energy causes water
molecules to go up and down.
Note that wavelength is defined as the distance
from one crest (or trough) to the next
Electromagnetic waves are invisible and can travel
through a vacuum
They do not need particles in order to travel. They
travel through a vacuum such as space, at the speed
of light (3.00 x 108 m/s)
Electromagnetic waves are very similar to water
waves. Both types of waves involve the movement of
energy from one point to another
Light spectrum
White visible light is made up of asequence of colours
called visible light.
Traditionally there are 7 colours red, orange, yellow,
green, blue indigo, and violet