# What is Light?.

## Presentation on theme: "What is Light?."— Presentation transcript:

What is Light?

Energy! What Is Light? Travels like a wave
A small packet of light energy is called a Photon What Is Light?

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

Characteristics of a Wave
Waves have high points called “crests.” Waves also have low points called “troughs.” The distance from one crest (or trough) to the next crest (trough) is called a “wavelength” 7

Arranged by wavelength and frequency on EM Spectrum
Wavelength: distance from peak to peak or trough to trough Frequency: the number of peaks that pass a point in a certain time span Also means cycles per second (measured in Hertz, Hz)

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

High frequency and short wavelength = HIGH ENERGY
Key facts High frequency and short wavelength = HIGH ENERGY

All waves shorter than visible light can cause cancer. UV - light - sun burn and skin cancer X-rays can cause cancer (that is why the dentist leaves the room when she X-rays your teeth) Gamma rays are the most dangerous they can kill ALL living things and cause cancer BUT also used to treat cancer because they destroy cancer cells

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.

Visible Region of the Electromagnetic Spectrum
Light we can see ROYGBIV – Acronym for: Red, Orange, Yellow, Green, Blue, Indigo, & Violet.  Largest to Smallest Wavelength. Click here to see a prism separating white light

- 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)

Let’s go see the sun under a spectroscope!

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 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

Try these: Draw 3 complete cycles of a wave that has a wavelength of 2.0 cm. Count the number of crests and troughs in the wave you drew from Q#1. Label each crest and trough. What characteristic(s) of a wave is used to arrange the waves in the electromagnetic spectrum? What is the visible spectrum? What does the acronym ROYGBIV stand for? How are you going to remember the order of the EM spectrum? TRUE or FALSE: Ultraviolet light has higher energy than microwaves? TRUE or FALSE: RED light has a shorter wavelength than BLUE light? Although gamma rays are very dangerous, they have a very important use. What are gamma rays used for?