ELECTROMAGNETIC WAVES AND THE EM SPECTRUM

MR. BANKS

8TH GRADE SCIENCE

ELECTROMAGNETIC WAVES

• Do not need matter to transfer energy.

• Made by vibrating electric charges.

• When an electric charge vibrates, the

electric field around it changes creating a

magnetic field.

• What type of wave is this?

ELECTROMAGNETIC WAVES

EM WAVES

• All matter contains charged particles that

are always moving; therefore, all objects

emit EM waves.

• The wavelengths become shorter as the

temperature of the material increases.

• EM waves carry radiant energy.

EM WAVE SPEED

• All EM waves travel

300,000 km/sec in

space. (the speed of

light!)

• EM waves usually

travel slowest in solids

and fastest in gases.

Material Speed

(km/s)

Vacuum 300,000

Air <300,000

Water 226,000

Glass 200,000

Diamond 124,000

REVIEW:

WAVELENGTH AND FREQUENCY

What did we already learn?

• Wavelength = distance from one point in the wave to the same point in the next.

• Frequency = number of wavelengths that pass a given point in 1 s.

• As frequency increases,

• The wavelength becomes smaller.

REVIEW

• What did we learn determined energy of

a wave?

• The Amplitude

THE PHOTOELECTRIC EFFECT

• In 1887, Heinrich Hertz

discovered that shining

light on a metal

caused electrons to be

ejected.

• Albert Einstein

explained Hertz’s

discovery: EM waves

can behave as a

particle and not a

wave, he named the

particles photons.

WAVE INTERFERENCE

WAVE DIFFRACTION

• Double slit experiment – looking for wave interference

LIGHT AS A WAVE

• Double slit

experiment –

looking for wave

interference

• The alternating

bands of light and

dark demonstrated

the “wave nature”

of light.

WAVE-PARTICLE DUALITY

• The theory that light sometimes behaves

like a wave and sometimes behaves like a

particle (photon)

THE EM SPECTRUM

• The whole range of EM wave frequencies

is called the electromagnetic spectrum.

• Different parts interact with matter in

different ways.

• The frequencies humans can see are

called visible light, a small part of the

whole spectrum.

RADIO WAVES• Radio waves are low frequency EM waves with

wavelengths longer than 1mm.

• These waves must be turned into sound waves

by a radio before you can hear them.

• Used for radio, TV, cell phones, and WiFi.

RADIO WAVES

• Most radio waves are not blocked by the

atmosphere.

MICROWAVES

• Microwaves are radio waves with wavelengths less than 30 cm (high frequency radio waves).

• Cell phones and satellites use microwaves between 1 cm & 20 cm for communication.

• Microwave ovens, use very high frequency/low wavelength waves to transfer energy to water molecules in the food causing them to vibrate and heat up.

CELL PHONE MICROWAVES

• Wait, am I cooking my head when I’m on

the phone?

• Not really.

0.2C temperature

rise

RADAR - RADIO DETECTING

AND RANGING• Uses radio waves to find the position and

speed of objects using wave reflection by

bouncing radio waves off the object.

MRI – MAGNETIC

RESONANCE IMAGING• Uses radio waves to

diagnose illnesses with a strong magnet and a radio wave emitter and a receiver. Protons in H atoms of the body act like magnets lining up with the field. This releases energy which the receiver detects and creates a map of the body’s tissues.

LONG RANGE COMMUNICATION

• Before satellites, the only way to communicate

long ranges wirelessly was to use short wave radio.

• Radio signals sent into the atmosphere at the right

wavelength would reflect back to earth at

extremely long ranges.

• Still used today to

send signals to remote

places.

SHORTWAVE RADIO ON THE

INTERNET

• http://websdr.ewi.utwente.nl:8901/

INFRARED WAVES

• EM waves with wavelengths between 1mm & 750 nm.

• Used daily in remote controls, to read CDs

• Every object gives off infrared waves.

• Hotter objects give off more than cooler ones.

THERMOGRAPHY

• Using the emission of infrared waves to

measure the temperature of something.

• Using the emission of infrared waves to

measure the temperature of something.

THERMOGRAPHY

• Using the emission of infrared waves to

measure the temperature of something.

THERMOGRAPHY

VISIBLE LIGHT

• Range of EM waves humans can see

• From 750 to 400 nanometers in length.

• You see different wavelengths as colors.

• Violet has shortest wavelength

• Red has the longest wavelength

• Light looks white if all colors are present

When light enters a new medium it bends (refracts).

Each wavelength bends a different amount allowing

white light to separate into its

various colors ROYGBIV.

FIBER OPTICS

• Uses pulses of light to send digital data over

large distances.

• Information literally travels at the speed of light.

• Makes up the primary backbone of the modern

internet.

ULTRAVIOLET LIGHT

• EM waves with wavelengths from about

400 nanometers to 10 nanometers.

• Have enough energy to enter skin cells

• Directly damages DNA

• Which can cause skin cancer

IONIZING RADIATION

• Causes harm to living things

THE OZONE LAYER

• 20-50 km above earth

• Absorbs most of the Sun’s harmful UV rays

• The ozone layer was decreasing due to

CFCs in AC, refrigerators, & cleaning

fluids, but it’s recovering.

THE OZONE LAYER

• Protects us from other harmful EM waves

• Without the ozone layer, even more harmful EM

waves would reach earth

X-RAYS

• Shorter wavelength than UV radiation

• Carries a large amount of energy

• Can pass through much more matter

• Large doses can cause harm deeper than

the skin

X-RAYS

• Bones and teeth can absorb X-Rays

GAMMA RAYS

• EM waves with the shortest wavelength

• Carries the greatest amount of energy

• Can pass the farthest through things

• Extremely harmful to living things

• Can be used in radiation treatments to kill

cancer cells.

• Must be very careful, or it could cause

much more harm than good.

GAMMA RAYS