Electromagnetic Waves &
the Electromagnetic Spectrum
Electromagnetic Waves
• Transverse waves without a medium!
• (They can travel through empty space)
• They travel as vibrations in
electrical and magnetic fields.
– Have some magnetic and some
electrical properties to them.
TRAVEL AT THE SPEED OF
LIGHT– around 300,000,000 m/s
–the speed of light!
(sound is 342m/s)
At this speed they
can go around the
world 8 times in one
second.
Electromagnetic Spectrum—name for the
range of electromagnetic waves when
placed in order of increasing frequency
RADIO
WAVES
INFRARED
RAYS
MICROWAVES
ULTRAVIOLET
RAYS
VISIBLE LIGHT
GAMMA
RAYS
X-RAYS
Notice the wavelength is
long (Radio waves) and gets shorter (Gamma Rays)
1. RADIO WAVES &
Microwaves
Have the longest
wavelengths and
lowest
frequencies of
all the
electromagnetic
waves.
Global Positioning Systems (GPS) measure the
time it takes a radio wave to travel from
several satellites to the receiver, determining
the distance to each satellite.
MRI
(MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a
magnet to create an image.
Radio Waves: Radio (music)
and Radar Guns
RADAR (Radio
Detection and
Ranging)
• Used to find the
speed of an object
by sending out radio
waves and measuring
the time it takes
them to return.
MICROWAVES
They are the
shortest radio
waves.
Used in microwave
ovens – to cook
food!
2. INFRARED RAYS
Infrared= below
red
Shorter
wavelength and
higher
frequency than
microwaves.
Below our
range of vision
INFRARED RAYS
Infrared rays
are used in
remote
controls and
other sensors
Reading the Heat loss of
homes
You can feel the
longest ones as
warmth on your
skin
Warm objects
give off more
heat energy than
cool objects.
3. VISIBLE LIGHT
Electromagnetic waves we
can see.
Longest wavelength= red
light
Shortest wavelength=
violet (purple) light
When light enters
a new medium it
bends (refracts).
Each wavelength
bends a different
amount allowing
white light to
separate into it’s
various colors
ROYGBIV.
4. ULTRAVIOLET RAYS
Shorter
wavelength and
higher
frequency than
visible light
Carry more
energy than
visible light
Used to kill
bacteria.
(Sterilization
of equipment)
Ultravioet Rays can damage skin!
Too much can cause skin cancer.
Use sun block to protect against
(UV rays)
5. X- RAYS
Shorter wavelength
and higher
frequency than UVrays
Carry a great amount
of energy
Can penetrate most
matter.
Bones and teeth absorb x-rays. (The light part
of an x-ray image indicates a place where the xray was absorbed)
Why the Lead Vest?
Ever have to wear
a lead vest at the
dentist or the
doctor???
X Rays so strong,
they can cause cancer
6. GAMMA RAYS
Shorter wavelength
and higher frequency
than X-rays
Carry the greatest
amount of energy
and penetrate the
most.
Used in radiation treatment to kill
cancer cells.
Can be very harmful if not used
correctly.
The Incredible
Hulk was the
victim of
gamma
radiation.
Exploding
nuclear
weapons emit
gamma rays.
Brief SUMMARY
A. All electromagnetic waves travel at the same
speed. (300,000,000 meters/second) in a
vacuum.
B. They all have different wavelengths and
different frequencies.
– Long wavelength-lowest frequency
– Short wavelength highest frequency
– The higher the frequency the higher the
energy.
TAKE OUT INTRO TO
WAVES HANDOUTS
FROM MONDAY
When Waves Hit Things
Reflection:
The wave bounces off the new medium and can
change direction
When Waves Hit Things
Reflection:
The wave bounces off the new medium and can
change direction
EXAMPLES?
ECHO
MIRROR
COLORS WE SEE
Refraction
Refraction:
The wave enters a new
medium and changes
speed
This is responsible for
“weirdness” when you
look at things through
water – magnification,
warping, etc…
Refraction
Refraction:
The wave enters a new medium and changes
speed
EXAMPLES?
Looking in a fish tank
Your voice sounds different to yourself than
when you hear it on a recording
Diffraction
Diffraction: The wave bends around
corners or edges of a barrier
Diffraction
Diffraction: The wave bends around corners
or edges of a barrier
EXAMPLES?
You see light from other room
You can hear someone from around a corner
TAKE 5 Minutes:
Label the parts and
match the definitions of
a Transverse wave and a
Longitudinal
(Compressional) Wave
Frequency of a wave
Frequency: the number of waves
that pass a point in a given amount
of time.
# of waves
f 
time
Measured in Hertz (Hz)
TEST THE
RELATIONSHIP BETWEEN
WAVELENGTH AND
FREQUENCY USING
SLINKYS
Go get your clicker!
What is the relationship
between wavelength and
frequency of waves?
Frequency Up
Wavelength?
Speed of Waves
Wave speed is equal to the frequency
of the wave times the wavelength.
Vw = f  λ (units: meters/second, or
equivalent)
Look at that formula – if Vw stays the same.
What can you say about f and λ?
Practice Practice Practice
1) A wave has frequency of 50 Hz
and a wavelength of 10 m. What is
the speed of the wave?
22/03/2016
Practice Practice Practice
2) A wave has frequency of 5 Hz and
a speed of 25 m/s. What is the
wavelength of the wave?
22/03/2016
3) A flute is played and hits a note with a
soundwave that is 512 Hz in frequency. The
speed of the sound in the air is 342 m/s
What is the length of the wave?
22/03/2016
CONSTRUCTIVE AND
DESTRUCTIVE
INTERFERENCE
CONSTRUCTIVE:
WAVES in sync make a bigger amplitude –
RESONANCE
remember this? resonance1
Check this out: Rubens Tube
CONSTRUCTIVE AND
DESTRUCTIVE
INTERFERENCE
DESTRUCTIVE:
WAVES with same frequency and wavelength
can cancel each other out if not in sync
SOUND!
Sound – as Waves
LONGITUDINAL (COMPRESSIONAL)
WAVES
SOUND WAVES MUST HAVE a
MEDIUM TO TRAVEL THROUGH.
Travel fastest in a solid. WHY AGAIN?
Sound – as Waves
Amplitude = volume
Frequency = pitch. High frequency, high
pitch. Low frequency, low pitch.
Lets try SOUND SIMULATOR
Measuring Sound
Decibel – a measure
of the Sound Pressure
Level. The higher the
decibel, the more
intense the sound.
Whisper Quiet Library at 6'
30dB
Normal conversation at 3'
60-65dB
City Traffic (inside car)
85dB
Level at which sustained
exposure may result in
hearing loss
90 - 95dB
Power mower at 3'
107dB
Listening to music with
headphones
105-120 dB (earbuds add 69 dB)
Pain begins
125dB
12 Gauge Shotgun Blast
165dB
Death of hearing tissue
180dB
Loudest sound possible
194dB
WHAT DID YOU SAY?
people using that standard earbud could
listen at about 80% of maximum volume
for 90 minutes per day or less without
increasing their risk for noise-induced
hearing loss. But the louder the volume,
the shorter your duration should be. At
maximum volume, you should listen for
only about 5 minutes a day.
Why am I telling you this?
PROTECT YOUR HEARING!!
Don’t go deaf!
August 27, 1883
Krakatoa
180 dB
Loudest
sound ever
heard.
The sound
itself caused
tsunamis
The Doppler Effect
The what?
The Doppler Effect Explained
The “perceived” change in frequency of an
object’s sound when the source and the
observer are in motion relative to each
other.
Draw an example:
Cool sound stuff…
Supersonic (faster than the speed of sound)
Subsonic (slower than the speed of sound)
Sonic boom (what happens when you pass
the speed of sound)
Infrasound (below 20 Hz)
Yay, Tuning Forks!
Look at the tuning forks I have given
you.
Locate someone near you with a
different sized tuning fork.
Compare the sounds of your two forks.
Which one is lower?
Now look at the forks and compare the
numbers…what do you think the
number stands for?
Before you go!
Take out a small piece of paper, put your
name on it.
Use the speed of sound 342 m/s and the
frequency of your tuning fork to find the
wavelength of the sound wave your
tuning fork makes.
(share fork with neighbor if they don’t have
one)