electromagnetic waves and the em …...em wave speed •all em waves travel 300,000 km/sec in space....
TRANSCRIPT
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