General Wave Properties

ByLeslie McGourty and Ken Rideout

All the information on waves that’s fit to print

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