The The Electromagnetic Electromagnetic

SpectrumSpectrum

April 3, 20007

So far we have talked about Mechanical Waves……

but there are some waves that don’t need a medium to travel

through…

We call these Electromagnetic waves (such as light) that

travel throughout “matter-less” space.

Radio

Microwaves

Infrared Ultraviolet

VisibleX-Ray

Gamma

Larger WavesLarger Waves Smaller WavesSmaller Waves

Light vs. Sound• Transverse

wave•Longitudinal wave

•Does not require a medium

•Frequency tells you the color•Amplitude tells you the brightness

•Requires a medium•Frequency tells you the pitch

•Amplitude tells you the loudness (decibels)

300,000 km/s 300,000 km/s (fast!)(fast!)

**As far as we know, **As far as we know, NOTHING travels faster NOTHING travels faster than the speed of light!!than the speed of light!!•Very fast

compared to the speed of sound (.340 km/s)

SpectrumSpectrum: the full range, in this case, the full range of light waves that can be given off by excited electrons.

•Arranges light waves based on their wavelength and frequency

Long wavelength = Low frequencyShort wavelength = High frequency

• ALL ALL electromagnetic electromagnetic waves travel at waves travel at the same the same SPEEDSPEED

Frequency Increases & Wavelength Decreases!Frequency Increases & Wavelength Decreases!

Lowest frequency and longest wavelength;

used for communication.

1.1. RADIO RADIO WAVESWAVES

•Very LONGLONG wavelengths•Radio and TV waves are regulated by the FCC (Federal Communications Commission) to reduce interference

•AM Radio waves have a longer wavelength (lower frequency) •FM Radio waves have a shorter wavelength (higher frequency)

Just Just FYI!! FYI!!

A higher energy radio wave; used for cooking

food

Water and fat absorb energy carried by microwaves

When these molecules move around faster they get hotter and give off heat

Microwaves are absorbed by molecules up to 2 cm below the surface (this is why food is sometimes cold in the middle! YUK!)

Just Just FYI!! FYI!!

•Used in radar because it penetrates rain and fog•Used by Cell phones• Does not occur naturally and is made by various forms of communication technology •SETI = Search for extraterrestrial Intelligence uses this frequency to search, because it is not made naturally

Just Just FYI!! FYI!!

Can’t be seen, but can be felt as heat.

2. 2. INFRARED WAVESINFRARED WAVES

Everything gives off infrared radiation; it

depends on the thermal energy

Infrared light is even used to heat food sometimes - special lamps that emit thermal infrared waves are often used in fast food restaurants!

•Examples of Infrared waves:

TV's remote control

Fire

Radiators

Infrared film to photograph a house to reveal areas in the structure that are leaking and wasting heat

Just Just FYI!! FYI!!

•Primary source of Infrared Radiation is heat or thermal radiation

Any object that has a temp. radiates in the infrared, even ice cubesEx. Charcoal is not burning but will emit heat

Just Just FYI!! FYI!!

• How Infrared radiation is used:– Snakes in the ‘viper’ family have sensory

“pits” that detect I.R., so they can detect warm-blooded prey

– Infrared pictures can be taken using special cameras and film that detects differences in temperature• Once the pictures are taken, they assign

different brightness or false colors to them to provide a picture our eyes can interpretJust Just

FYI!! FYI!!

Part of the spectrum you CANCAN see.

R R O O YY GG B B I I VV

3. 3. VISIBLE LIGHTVISIBLE LIGHT

The color of visible light depends on its frequency

Present in sunlight and have enough energy to

kill living cells

4. Ultraviolet Light (UV)

•Invisible to the human eye

•Some insects, like bumblebees, can see them

UV Light is used:

In Tanning beds

To sterilize surgical equipment

In Food processing

Just Just FYI!! FYI!!

•Ozone absorbs highest energy UV light

•UV Light can cause sunburns and eventually malignant melanomas

•Enough energy to pass through most materials (skin)

5.5. X-Rays X-Rays

• Lead is one material that X –Rays cannot pass through

•X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen, a German scientist

•He found them quite by accident when experimenting with vacuum tubes.

•Also can be created by a machine like those for medical x-rays Just Just

FYI!! FYI!!

•The Earth's atmosphere is thick enough that virtually no X-rays are able to penetrate from outer space all the way to the Earth's surface

•Originate in nature deep in space in the hot nebulae of stars

Just Just FYI!! FYI!!

•bones and teeth are dense and absorb more X-rays then your skin does

•silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent

When X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film

•Metal absorbs even more X-rays - can you see the filling in the image of the tooth

Just Just FYI!! FYI!!

Has the HighestHighest energy of allall of the electromagnetic waves

6. 6. Gamma RaysGamma Rays

Emitted by radioactive materials

Used to treat cancer,

Can go through concrete!

•Smallest wavelengths and possess more energy than any other wave in the electromagnetic spectrum

Produced by the hottest regions of the universe

•They are produced by:

violent events as supernova explosions or the destruction of atoms

The decay of radioactive material in space

Neutron stars and pulsars, and black holes

radioactive atoms and nuclear explosions

Just Just FYI!! FYI!!

•Medical Uses:Radioactive Tracers (put into a patients body and followed as it goes through)

A patient with lung problems can breathe in Xenon-133, a gas that emits gamma raysA special camera is used to take picturesThe patient isn’t injured by the radiation because they quickly breathe out all the gas

RadiotherapyTreatment of cancer

Just Just FYI!! FYI!!