Unit 3: Physics Light and Applications of Optics December 4, 2018 Unit 3: Physics Light and Applications of Optics Text: p. 463 - 477

What would Earth be like without light from the Sun? Sunlight is the energy that makes life possible on Earth. The Sun is our closest star—about 1.50 X 106 km from Earth. That is nearly 400 times farther than the Moon.

The nuclear reactions that occur within the Sun produce tremendous amounts of energy. One form this energy takes is light, which the Sun emits in all directions through the vacuum of outer space.

For centuries, scientists have tried to understand the nature of light and its properties. Some of these properties are easily observable, For example, light travels at a very high speed. When you turn on the light switch in a room, the room immediately fills with light. Scientists call a small packet of light energy a photon.

Light also travels in straight lines… When you turn on a flashlight in a dark room with dust in the air, you can see a beam of light travelling in a straight line.

Light-An Electromagnetic Wave Recall that heat energy can be transferred by either conduction or convection. Conduction and convection require a medium for transmission. A medium is: any physical substance that acts as a carrier for the transmission of energy.

Light, however, travels through the vacuum of outer space. This means that light does not require a medium for transmission.

WHAT IS LIGHT? A wave of electric and magnetic fields.

What is a wave? A wave is something that carries energy. Oscillates up and down creating crests and valleys with varying frequency.

What is an Electric Field? The space surrounding a stationary electric charge that exerts a force on other electrically charged objects.

Remember the “Pith-ball”?? + - Force of attraction + - Light Wiggle the charge… Now wiggle it at 1014 times and you get… Creation of an EM Wave

Types of Light (Electromagnetic) Waves: The Electromagnetic Spectrum Low energy, long waves High energy, short waves Sun relative size to Earth #11 Coronal Mass Ejection with Magnetic protection #18

White light is composed of a continuous spectrum of colours.

Sources of Light: Luminous: An object that gives off its own light. Non-Luminous: An object that does not give off its own light.

Luminous Sources of Light: Incandescence: Light given off due to high temperature. Actually invented by two Torontonians (Evans and Woodward) in 1874 using a carbon filament and N2 gas instead of tungsten. They tried to market the product with no success! Edison bought the patent to combine with his work and the rest is history.

Fluorescence: Chemical that gives off light when hit by invisible high energy light waves. * Electricity excites the Mercury vapour and causes the release of UV light. * The UV strikes the inner fluorescent coating to produce visible light. * Bad for landfill because of the Mercury.

Phosphorescence: * Chemical that gives off light when hit by high energy light waves, and stay luminous for long periods of time. (Glows in the dark.) * Phosphors absorb light (primarily UV) and give off visible light for varying periods of time.

Chemiluminescence: -Chemical reactions that give off light with next to no heat (cold light). -When living things produce the chemical it is called bioluminescent.

Triboluminescence: When certain crystals (sugar) are scratched, crushed or rubbed, light can be produced.

LEDs: Light emitting Diodes small lights that do not get too hot when they give off light. Inside, they are made of small crystals of silicon that light up when electricity flows in the proper direction. Why LEDs are better than other sources of light: They do not waste energy as heat. They do not use mercury. They last a long time.

Lasers are a very powerful source of light. They have some special properties such as: The light is very intense (bright). The light is all the same colour (electromagnetic waves of the same energy level). The beam of light stays together as a beam (Waves are exactly in unison). FYI: *Lasers have been directed at the Moon to measure Earth-Moon distance at a distance of 385 000 km with an accuracy of 3 cm Uses of Lasers LASERS Video 50 min