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 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

FrequencyNumber 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

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

h

p

mv

h

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 WavesWavelength 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 (6.63 x 10 - 34 Js)

E is the energy of a photon in Joules

E

hc

f

c

What is this “photon” term you’re throwing in there?A photon is a bundle (quantum) of lightA 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 SpectrumThink 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 WAVESGAMMA 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-RAYSEmitted 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 LIGHTWhite 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 WAVES10 cm- 100,000+m

 in length Only cosmic waves

the reach the surface of the Earth

Cause of noiseDivided into smaller

frequency dependent groups called bands  

Used for communications

Sources:  transmitters and sparks from motors

PolarizationElectric and magnetic fields which make up

wave have preferred directionCan be horizontal, vertical, circular, or

ellipticalMost radio emission is unpolarizedTo learn more click here

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