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

Travels in straight lines. Travels VERY fast. - travel at a speed of Properties of Light Travels in straight lines. Travels VERY fast. - travel at a speed of 3.00 X 108 m/s

Electromagnetic Waves An 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 Spectrum Gamma rays X-rays Ultraviolet light Visible light Infrared light Microwaves Radio waves (pg. 466)

But we don’t see radio waves and x-rays…..

Our ears can not hear some high sound frequencies that dogs can. Radiometer and hot iron E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum 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 Sir Isaac Newton’s full name with title is easy to remember because of his initials (i.e. SIN)

Similarly…. A rainbow appears in the sky from the sun’s rays.

So….when light from the sun is broken down, its’ spectrum looks like 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 The sun’s light is therefore White Light.

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

The Visible Light Spectrum is a very small part of a much larger spectrum called the Electromagnetic Spectrum E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum

How Do You Remember the Colours? All the colours spell the name Roy G Biv (but that’s boring!)

Words to remember the Electromagnetic Spectrum from Long to Short Wavelength Radio Waves Microwaves Infra Red Visible Spectrum Ultra Violet X-Rays Gamma Rays Raul's Mother Is Visiting Uncle Xavier's Garden Rabbits Mate In Very Unusual eXpensive Gardens Raging Martians Invade Roy G. Biv. Using X-rays & Gamma Rays E3.2 identify and label the visible and invisible regions of the electromagnetic spectrum

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 box 2 prisms Draw what you see under the light rays!

Vocabulary! Medium, Convection, Conduction Radiation Electromagnetic Wave Electromagnetic Spectrum Visible Light Prism

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.