Geometric Optics

1. 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

2. What is Light? • Almostanything 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

3. 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

4. Some facts about Light • light is a type of energy This calculator doesn’t need a battery to keep going. Just plenty of sunlight

5. Lightwavescan travel throughemptyspace • 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

6. 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

7. 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

8. 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

9. 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

10. How is lightproduced? • 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

11. 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

12. Demonstration of source of lightusingdischarge 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

13. 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.

14. Note that wavelength is defined as the distance from one crest (or trough) to the next

15. 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

16. Lightspectrum 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