View
48
Download
0
Category
Tags:
Preview:
DESCRIPTION
General Wave Properties. Taken from ed links. What is a wave?. A wave is a transfer of energy from one point to another via a traveling disturbance A wave is characterized by its wavelength, frequency, and amplitude. Transverse . Waves that travel perpendicular to the direction of motion - PowerPoint PPT Presentation
Citation preview
General Wave Properties
Taken from ed links
What is a wave?
• A wave is a transfer of energy from one point to another via 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 wavesfor 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
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)
vf Traveling Waves move through space at a certain speed
Matter / Quantum Waves • Electrons and other tiny particles show wave-like
properties • A particle moving close to the speed of light (c)
can diffract or bend around the edges of objects• Also, particles do exhibit interference which is a
wavelike property • Any moving matter has wave characteristics in
theory BUT the wavelength of any life-size particle, like a golf ball, is so small that it is negligible
• To learn about matter waves in depth go on to the next slide; if not click
If we can sometimes consider an electron to be a wave, what is its
wavelength?
Its wavelength depends on its momentum
or
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
hp
mvh
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 - 34 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
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 :
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 HertzAnd h is Planck’s constant (there it is again- do you remember its value?) E is the energy of a photon in Joules
Ehc
fc
What is this “photon” term you’re throwing in there?
• A photon is a bundle (quantum) of light• A photon has energy equal to
Recall that h is Plank’s constant ν is the frequency of the radiation (wave)
hE
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 (x-ray 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, 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:
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 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- 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: transmitters 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
x
yElectric Field
Magnetic Field
Electromagnetic Wave
x
y
zE
Horizontal Polarization
Electric Field
Magnetic Field
Electromagnetic Wave
x
y
z
E
Vertical Polarization
Why Do We Care About Radio Waves?
• Gadgets- cell phones, microwaves, remote controls, garage door openers
• Science- radio astronomy, atmospheric research
Recommended