Waves disturbances

(but in a good way! Mostly )

Definition

Tuesday July 15, 2014 Waves 2

Waves are disturbances that transfer energy!

Types of Waves

Mechanical Waves

• A mechanical wave is a disturbance that propagates through a medium.

• A medium is any material (matter) through which a wave travels.

Mechanical wave examples: sound; water waves; a pulse traveling on a spring; earthquakes; a “people wave” in a football stadium.

Electromagnetic Waves

• An electromagnetic wave is simply light of a visible or invisible wavelength.

• Oscillating intertwined electric and magnetic fields comprise light.

• Light can travel without a medium—super, duper fast.

Tuesday July 15, 2014 Waves 3

Types of Mechanical Waves

Longitudinal Transverse

Tuesday July 15, 2014 Waves 4

Particle motion moves perpendicular to the direction

of wave propagation (wave motion)

Examples: Sound WavesSeismic waves that travel through the earth

Particle motion moves parallel to wave propagation

(wave motion)

Examples:Light wavesSeismic waves that travel on the surface of the earth

Types of Waves

Tuesday July 15, 2014 Waves 5

Use your slinky to model longitudinal and transverse

waves

Wave Characteristics

Tuesday July 15, 2014 Waves 6

WaveCycle

Wave cycleOscillation

Wave Characteristics

Tuesday July 15, 2014 Waves 7

• Amplitude (A) – Maximum displacement of particle of the medium from its equilibrium point. The bigger the amplitude, the more energy the wave carries.

(In the case of sound Large Amplitude = LOUD) (In the case of a radio wave

Large Amplitude = great signal strength!)

Wave CharacteristicsPeriod and frequency

• Period (T) – time required for 1 complete wave cycle (measured in seconds).

• Frequency (f) - The number of cycles passing by in a given time. The SI unit for frequency is the Hertz (Hz), which is one cycle per second.

(the number of waves that occur in 1 second)

T = 1/f

Tuesday July 15, 2014 Waves 8

Period-Frequency Relationship

Tuesday July 15, 2014 Waves 9

Beach example Suppose you were at the

beach and noticed the waves were hitting your toes at a regular repeating interval. You counted 5 waves touching your toes in 10 seconds time.

(Tip: Use your definitions!)• Determine the

frequency of the waves.

• Calculate the period of the waves.

Tuesday July 15, 2014 Waves 10

Wave Characteristics

Tuesday July 15, 2014 Waves 11

• Wavelength () – Distance from crest (max positive displacement) to crest, measured in meters.

• Frequency (f ) – The number of cycles passing by in a given time. The SI unit for frequency is the Hertz (Hz), which is one cycle per second.

• Wave speed (v) – How fast the wave is moving (the disturbance itself, not how fast the individual particles are moving, which constantly varies). The speed of all waves depends on the medium.

Wave RelationshipsWave-Speed

• Wavelength (λ)• Frequency (f)• Propagation speed (v)

v = λfRearrange this equation to solve

for wavelength.

λ = v/f

Example: Sound

The speed of sound at 25 °C (about room temperature) is 346.13 m/s. Assume you are playing the piano and strike middle C (frequency 261.6 Hz).

• Calculate the wavelength of middle C.

• Determine the period of this sound wave.

Tuesday July 15, 2014 Waves 12

Electric Charges

The atom

Tuesday July 15, 2014 Waves 13

Electric field lines

Tuesday July 15, 2014 Waves 14

Electromagnetic Waves

Tuesday July 15, 2014 Waves 15

Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields.

E field simulation

Tuesday July 15, 2014 Waves 16

Check out this simulation on electric fields https://phet.colorado.edu/en/simulation/charges-and-fields

Electromagnetic Waves

Tuesday July 15, 2014 Waves 17

Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields.

EM Transmission

Tuesday July 15, 2014 Waves 18

Check out these simulations to relate electric fields to how your CricketSat works.

• http://www.cabrillo.edu/~jmccullough/Applets/Flash/Optics/EMWave.swf (this one runs automatically)

• https://phet.colorado.edu/en/simulation/radio-waves (this one you control)

Speed of Light (c)

Example: Suppose your partner were on the moon and you were able to make a cell phone call directly to the moon. How long would it take the signal to make it from your phone on Earth to your partners phone on the Moon?

c = 3 x 108 m/s

Tuesday July 15, 2014 Waves 19

Your CricketSat

• Calculate the wavelength of the radio wave that your 433 MHz transmitter is transmitting.

• Assuming that your CricketSat makes it to 5 km in altitude – determine the time required for the 433 MHz signal to reach your ground station.

Tuesday July 15, 2014 Waves 20

M = Mega = 106 = 1 millionk = kilo = 103 = 1 thousand

EM Spectrum

Tuesday July 15, 2014 Waves 21

Atmospheric Opacity

Tuesday July 15, 2014 Waves 22

Where do the radio waves transmitted by our radio fall into this picture?Do we need to worry about atmospheric absorption?

The Visible Portion

EM Spectrum

Tuesday July 15, 2014 Waves 23

Make a statement about the percentage of visible light in the entire EM Spectrum

Waves 24Tuesday July 15, 2014

Frequency allocation chart

Tuesday July 15, 2014 Waves 25

Tuesday July 15, 2014 Waves 26