LIGHT AND THE ELECTROMAGNETIC

SPECTRUM

SECTION 4.3

Objectives

By the end of the lesson you should be able to:

Describe the electromagnetic spectrumGive everyday examples of uses of the

EMS

Waves…..they are all around you!!

No matter where you are, you are surrounded by invisible waves

What kind of waves are around you right now?

To Visible Light and Beyond!!!

Light spreads out or radiates from the Sun and other stars in all directions

Energy, like light, that travels by radiation is often called radiant energy

Not only does the Sun radiate visible energy (light), is also radiates invisible energy……..let’s take a deeper look….

Solar Radiation

Electromagnetic Radiation

How is a light wave different from a wave that travels through water?

In a water wave – water particles vibrate up and down as the wave passes through the water

In a light wave, electric and magnetic fields vibrate

Therefore: light is classified as electromagnetic radiation

Electromagnetic Radiation

Electromagnetic radiation is the transmission of energy in the form of waves that extend from the longest radio waves to the shortest gamma rays

Electromagnetic waves are described by different names depending on their frequency and wavelength

Electromagnetic Spectrum

Different waves have different wavelengths and frequencies

On this spectrum – the longer the wavelength, the lower the frequency

Radio waves have the longest wavelength and the lowest frequency

Gamma rays have the shortest wavelength and the highest frequency

Electromagnetic Spectrum

Wavelengths longer than visible light…..

The electromagnetic waves we can see with our eyes are only a small part of the entire spectrum

Different devices have been developed to detect other frequencies – what kinds of examples can you think of?

Radio waves – are detected by the antenna of your radio

Radio Waves

Radio waves are a type of electromagnetic radiation that have the longest wavelength and lowest energy and frequency

There are different uses for the different wavelengths of radio waves:

Radio broadcasting TV broadcasting

Microwaves and radar are types of radio waves

Other uses for Radio Waves

MRI – magnetic resonance imaging – long radio waves that are used to help us see inside our bodies and diagnose illnesses without having to do surgery

In an MRI – you lie in a large cylinder that has a powerful magnet, a radio wave emitter and a radio wave detector

The particles in your bones and soft tissues act like tiny magnets which can be lined up

The MRI machine causes the particles to flip and they then produce radio waves

This is detected by the receiver and is used to create a map of the different tissues – eg: brain, knee

Microwaves

Shortest wavelength and the highest frequency of all the radio waves

How do microwave ovens work? They use a specific wavelength of microwave

that is strongly absorbed by water particles When these water particles in the food absorb

microwaves, they begin to vibrate quickly and become hot only food with water particles can be heated using microwaves

Microwaves – other uses

Microwaves can also be transmitted to satellites that orbit Earth

These satellites receive the signals, strengthen them and retransmit them – as a way of communicating

Radio telescopes can be pointed at distant planets and galaxies and scientists study the radio waves to learn more about the composition, motion and structure of these objects

Radar

Shorter wavelength microwaves are used in radar – remote sensing

Microwaves are beamed out through the air and waves reflect from an object which can then show the location and speed of the object

We use radar for tracking the movement of cars, aircraft, watercraft and spacecraft

Radar

We also use radar for weather forecastingRaindrops, snow and other objects in the

air reflect radio wavesA device like Doppler radar, converts the

reflected radio waves into pictures that show the location and intensity of precipitation and the speed of the wind

RADARSAT

RADARSAT: a Canadian satellite that sweeps the ground below with radio waves

These waves can penetrate haze, fog, clouds and rain

What are some of the things RADARSAT can do? (check page 156 and list some on your notes)

Infrared Waves

Infrared waves are a type of electromagnetic radiation that have a longer wavelength, lower energy and frequency

You use them everyday! Examples: remote control, computer and CD-

ROMs Also referred to as heat radiation EVERY object emits infrared waves because

ALL objects contain some heat energy Warmer objects emit more infrared waves than

cooler objects

Uses for Infrared….

Look at the picture of the cat on page 157Which parts of his face are the warmest?Infrared images are used at some airports

to determine whether passengers coming from other countries have a fever (what would that signal?)

LANDSAT uses infrared to observe crops, forests and monitor damage by fire, insects, disease

Wavelengths Shorter than Visible Light…

These wavelengths carry more energy than those waves in the visible region

Includes: Ultraviolet waves X rays Gamma rays

Ultraviolet Waves

Ultraviolet waves are a type of electromagnetic radiation that have a shorter wavelength and higher energy and frequency

This radiation is very energeticWhen is hits your skin – it enables your

body to make Vitamin D – need for healthy bones and teeth!

Overexposure sunburns, skin cancers

Other uses for UV waves

Think CSI………Police sometimes use fluorescent powder

to study fingerprintsAlso – used to kill bacteria in food, water

and medical supplies

X rays

X rays are a type of electromagnetic radiation that have a really short wavelength and high energy and frequency

Discovered by Wilhelm Roentgen, they are used to photograph teeth and bones

Other uses for X rays….

Low doses are used by doctors and dentists

People working with X rays protect themselves from harmful radiation

X ray screening devices are used by airport security to examine luggage

Also used to inspect for cracks inside jet engines without taking the engine apart

Gamma Rays

Highest energy and frequency and shortest wavelength

Result from nuclear reactions and are produced by the hottest regions of the universe

Focused bursts of these rays are used in radiation therapy to kill cancer cells