What is Light?

What Is Light?

Energy!

Energy.Usually needs a medium for transmission.Ex. Heat transfers by

convection or conduction.

Light Energy..Travels through the vacuum of outer space..Transferred by radiation in the form of an electromagnetic wave

Properties of LightTravels in straight lines.Travels VERY fast.- travel at a speed of

3.00 X 108 m/s

Electromagnetic WavesAn electromagnetic wave is a wave of energy that moves through space

Different electromagnetic waves have different lengths which give them different amounts of energy

Electromagnetic Spectrum

Electromagnetic SpectrumGamma raysX-raysUltraviolet lightVisible lightInfrared lightMicrowavesRadio waves (pg. 466)

But we dont see radio waves and x-rays..

Our ears can not hear some high sound frequencies that dogs can. Similarly our eyes can not see some of the wavelengths of light.

Visible Light!Any electromagnetic wave that the human eye can detect.Called the Visible Spectrum.

- white light breaks into the colours of a rainbow when it passes through a prism.- white light is made of all the colours of the visible spectrum

Similarly. A rainbow appears in the sky from the suns rays.

So.when light from the sun is broken down, its spectrum looks likeThe suns light is therefore White Light.

When light from some sources is broken down, its Spectrum looks like a series of lines.

The Visible Light Spectrum is a very small part of a much larger spectrum called the Electromagnetic Spectrum

How Do You Remember the Colours?All the colours spell the name

Roy G Biv

(but thats boring!)

Words to remember the Electromagnetic Spectrum from Long to Short Wavelength

Radio Waves Microwaves Infra Red Visible Spectrum Ultra VioletX-Rays Gamma Rays Raul'sMotherIsVisitingUncleXavier'sGardenRabbitsMateInVeryUnusualeXpensiveGardensRagingMartiansInvadeRoy G. Biv.UsingX-rays& Gamma Rays

Las Vegas Light Show

What is BLACK Light?A lamp that emits electromagnetic radiation almost exclusively in the soft near ultraviolet range.Only a very small fraction of visible radiation is emitted, and it is seen as violet/blue light!

Playing with Light!Ray box2 prismsDraw what you see under the light rays!

Vocabulary!Medium, Convection, ConductionRadiationElectromagnetic WaveElectromagnetic SpectrumVisible LightPrism

Homework!

Pg. 469 # 2 - 9

Newton noted that the individual coloured lines could not be separated further.

These lines are pure colours and are identified by a frequency and wavelength number.

*********Radiometer and hot iron

E3.2identify and label the visible and invisible regions of the electromagnetic spectrum

**Sir Isaac Newtons full name with title is easy to remember because of his initials (i.e. SIN) **Encourage students to make up their own mnemonic for remembering the order of rainbow colours.Let them know A mnemonic is just a way to remember simple lists

To show students a very good full spectrum see http://isaac.exploratorium.edu/~pauld/summer_institute/summer_day6color/color_diffraction_grating.html

Note the Capital letters denote the Additive Primary colours. More on this later in Seeing Colour.ppt

Isaac Newton named the colors of the spectrum we use today. At first he only identified 5 colours (red, yellow, green, blue, violet) He changed this to seven colors out of a mistaken belief, derived from the ancient Greeks. They believed there was a connection between the colors, the musical notes, the known objects in the solar system, and the days of the week. Newton therefore added Orange and Indigo to make up 7 names for the main colours of he spectrum i.e. ROYGBIV, Red, Orange, Yellow, Green, Blue, Indigo, Violet*Students will benefit by viewing various light sources including Spectrum Tubes through Spectroscopes. This will clearly demonstrate most light is really made up of a series of pure colours*E3.2identify and label the visible and invisible regions of the electromagnetic spectrum**E3.2identify and label the visible and invisible regions of the electromagnetic spectrum*****