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 wavesthrow 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