Transcript Waves in Motion

What is a wave?
 A wave is a transfer of energy from one point
to another by a traveling disturbance
 A wave is characterized by its wavelength,
frequency, and amplitude
Transverse
 Waves that
travel
perpendicular to
the direction of
motion
 Examples: Light,
-p waves
for earthquakes,
Ocean waves
Longitudinal
 Waves that travel
parallel to the direction
of
motion
 Made up of
compressions and
rarefactions in the
medium that they are
traveling in
 Examples: sound
waves and s waves for
earthquakes
Do You See The
Difference Between
Transverse And
Longitudinal Waves?
Wavelength (λ)
 Distance from
successive crest to
crest or trough to
trough
 Measured in meters
Frequency
 Number of crests
passing by per
second
 Measured in Hertz
(Hz) defined to be
one cycle per sec
 Equal to the inverse
of the amount of
time it takes one
wavelength to pass
by
Amplitude
 Maximum
displacement of the
wave
 The amplitude will
have different units
depending on the type
of wave
 In a sketch of the
wave, it is the distance
from the middle of the
wave to the peak
Wave Speed
Traveling Waves move through space at a certain speed
 f v
Where,
v is the speed of the wave (m/s)
λ is the wavelength in meters (m)
f is the frequency in Hertz (cycle/s)
Its wavelength depends on its
momentum
p
h

or
h

mv
where p is momentum in kg*m/s, h is Planck’s
constant = 6.63 x 10-34 J, and λ is the
wavelength in meters
What is Planck’s constant?
 Planck’s Constant is the size where
quantum mechanics becomes necessary
 Since "Planck's Constant" (‘h’= 6.63 x 10
-
Js) is such a tiny number, quantum
mechanics is needed only at very small
scales
 An electron also has spin that is quantized
in units of h.
 These units (Joule-sec) are units of
angular momentum
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Electromagnetic Waves
 Waves of energy emitted from any accelerating




charges
Any object that is above absolute zero emits
electromagnetic waves
The entire range of possibilities is called the
“Electromagnetic Spectrum”
Still confused? Then click What are
electromagnetic waves?
To learn about the wavelength of photons click to
the next slide. To move onto the EM spectrum
click
Electromagnetic Waves
 Wavelength is :
c hc
 
f
E
Where,
c is the speed of light (3 x 108 m/s in a vacuum)
λ is the wavelength in meters
f is the frequency in Hertz
And
h is Planck’s constant (6.63 x 10 - 34 Js)
E is the energy of a photon in Joules
What is this “photon” term you’re
throwing in there?
 A photon is a bundle (quantum) of light
 A photon has energy equal to
E  h
Recall that
h is Plank’s constant
ν is the frequency of the radiation (wave)
What does a photon do?
 Both magnetic and
electric forces
involve the
exchange of
photons
 The photon has
zero rest mass, but
has momentum,
can be deflected
gravity, and can
exert a force
The Electromagnetic
Spectrum
 Think you know all about the electromagnetic
spectrum? Well take a tour of the
Electromagnetic Spectrum to find out more
cool information. Then, if you’re brave
enough, take the electromagnetic quiz.
Remember to run the applet at the top of the
page.
 If you still need more help review the next 7
slides. If not click
TYPES OF ELECTROMAGNETIC
WAVES
GAMMA RAYS
 Emitted from the nuclei
of atoms during
radioactive decay or
during high-speed
collisions with particles.
 Ionizing
 Used in cancer treatment
and for sterilization
Sources: Cobalt 60, the
inner core of the sun
X-RAYS
 Emitted when an electron
moves from certain
excited states back down
to its ground state, or
when an electron that is
moving very quickly is
suddenly stopped
 Two groups - long
wavelength (soft x-rays)
and shorter wavelength
(hard x-rays)
 Used for radiography (xray photography) and to
look at materials in
industry for defects
 Sources: emitted by
heavy atoms after
bombardment by an
electron
ULTRAVIOLET
 Above the color violet
 Three groups - UV A,
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UV B, and UV C.
“A” type: longest
wavelength; least
harmful
UV B and UV C are
absorbed by DNA in
cells
Used by the body to
produce vitamin D, to
kill bacteria on
objects, and for sun
tanning
Sources: Ultra hot
objects 5000°C or
more
VISIBLE LIGHT
 White light:
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combination of
all the colors
Rainbow:
example of white
light that has
been separated
into a continuous
spectrum of
colors
The names of
colors are
assigned in order
of their
wavelengths
Used for
communications
(fiber optics)
Sources: very
hot objects
Color
Wavelength interval Frequency interval
red
~ 625 to 740 nm
~ 480 to 405 THz
orange ~ 590 to 625 nm
~ 510 to 480 THz
yellow
~ 565 to 590 nm
~ 530 to 510 THz
green
~ 520 to 565 nm
~ 580 to 530 THz
cyan
~ 500 to 520 nm
~ 600 to 580 THz
blue
~ 430 to 500 nm
~ 700 to 600 THz
violet
~ 380 to 430 nm
~ 790 to 700 THz
INFRARED
 Thought of as heat but
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is not always
Far infrared energy is
heat energy.
All objects that have
warmth radiate
infrared waves
Easily absorbed and
re-radiated.
Used in remote
controls, surveillance,
therapy of muscles
Sources: Humans,
the sun
MICROWAVES
 1 mm-1 dm in length
 Absorbed by water
molecules – how
microwave ovens heat
food
 Used in
telecommunications
and power
transmission
 Sources: electric
circuits, many stars,
microwave ovens
RADIO WAVES
 10 cm
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
100,000+m in
length
Only cosmic waves
the reach the
surface of the Earth
Cause of noise
Divided into smaller
frequency
dependent groups
called bands
Used
for communications
Sources: transmitte
rs and sparks from
motors
Polarization
 Electric and magnetic fields which make up
wave have preferred direction
 Can be horizontal, vertical, circular, or
elliptical
 Most radio emission is unpolarized
 To learn more click here
Polarization
y
Electric Field
Electromagnetic Wave
Wave
Magnetic Field
x
Horizontal Polarization
Vertical Polarization
y
y
E
x
z
x
E
z
Why Do We Care About Radio
Waves?
 Gadgets- cell phones, microwaves, remote
controls, garage door openers
 Science- radio astronomy, atmospheric
research