General Wave Properties

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# General Wave Properties - PowerPoint PPT Presentation

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

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## General Wave Properties

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Presentation Transcript

### General Wave Properties

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
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

Where,

v is the speed of the wave (m/s)

λis the wavelength in meters (m)

f is the frequency in Hertz (cycle/s)

Matter / Quantum Waves
• Electrons and other tiny particlesshow 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
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

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 Hertz

And

h is Planck’s constant (there it is again- do you remember its value?)

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

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 (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
INFRARED
• Thought of as heat but is not always
• Far infrared energy is heat energy.
• All objects that have warmth radiate infrared waves
• 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
• 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

y

Electric Field

Electromagnetic

Wave

Magnetic Field

x

y

Vertical Polarization

Horizontal Polarization

y

E

x

z

x

E

z

Polarization

Electric Field

Electromagnetic Wave

Magnetic Field