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Electromagnetic Waves
Electromagnetic Waves
• Electromagnetic Waves
– Made by vibrating
electric charges
– Can travel through space
where matter is not
present
– We cannot hear them,
but can feel and
experience their effects
• Vibrations of Electric
Charges
Electromagnetic Waves
• Electromagnetic Waves
– Travel by transferring
energy between
vibrating electric and
magnetic fields
– Like some mechanical
waves, electromagnetic
waves are considered
transverse
Electric and Magnetic Fields
• Electric Fields
– Electric field surrounds
all electric charges
– Electric Field Lines
• Magnetic Fields
– Magnetic field surrounds
all magnets
– Magnetic Field Lines
Electric and Magnetic Fields
Making Electromagnetic Waves
• Electric charges vibrate
• Electric field around it
changes
• The magnetic field
around the charge
changes
• Both fields change
continuously creating
the wave
Making Electromagnetic Waves
• Electromagnetic Waves
• Making of
Electromagnetic Wave
Properties of Electromagnetic Waves
• All objects contain
charged particles
• All objects emit
electromagnetic waves
• Radiant Energy
– Energy carried by EM
waves
Properties of Electromagnetic Waves
• Wave speed
– Travel at 300,000 km/s in
the vacuum of space
– Called “speed of light”
– Usually travel slowest in
solids
– Travel fastest in gases
Properties of Electromagnetic Waves
• Wavelength and
Frequency
– Crest to crest
– As frequency increases,
wavelength decreases
Waves and Particles
• Em waves
– Can behave like particles
– This is why energy depends
on frequency, not
amplitude
• Photons
– Particles of
electromagnetic waves
– Carrier of electromagnetic
radiation
Electromagnetic Spectrum
• Frequency range
– Wide variety of
frequencies
– Entire range is known as
the electromagnetic
spectrum
Radio Waves
• Lowest frequency on
the spectrum
• Can’t see or hear
• Functions:
– Carry radio waves
– Used by some cell phone
towers
– RADARs (Radio Detecting
and Ranging)
– MRIs
Microwaves
• Little shorter
wavelengths than radio
waves
• Functions
– Cell phone towers
– Satellite signals
– Microwave ovens
Infrared Waves
• Shorter wavelengths
than radio or
microwaves
• Functions
– Transmits thermal
energy
– Remote controls
– CD-ROMs are read by
infrared waves
– Infrared imagery
Visible Light
• Only part of the
spectrum we can see
• ROY G BIV
Ultraviolet Waves
• Can enter skin cells
• Overexposure can cause
skin damage and cancer
• UVA and UVB waves
• Functions
– Kills bacteria on objects
such as food or medical
supplies
– Make some materials
fluoresce (CSI)
X-Rays
• Can penetrate skin
• Functions
– X-rays of bones and
teeth
– At airport to screen
luggage and other
devices
Gamma Rays
• Shortest wavelength of
the spectrum
• Functions
– Radiation therapy in
which gamma rays kill
diseased or cancerous
cells
Radio Communication
• Radio Transmission
– Each station assigned a
certain frequency
– Carrier Wave
• Specific frequency of the
electromagnetic wave
assigned to a station
AM Radio
• AM Radio
– AM = amplitude
modulation
– Broadcasts by varying
the amplitude of the
carrier wave
– AM carrier range from
frequencies of 540,000
to 1,600,000 HZ
FM Radio
• FM Radio
– FM = Frequency
Modulation
– FM broadcasts by
changing the frequency
of the carrier wave
– Frequencies range from
88 million to 108 million
Hz