Waves disturbances (but in a good way! Mostly )

Definition Tuesday July 15, 2014Waves2 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, 2014Waves3

Types of Mechanical Waves Longitudinal Transverse Tuesday July 15, 2014Waves4 Particle motion moves perpendicular to the direction of wave propagation (wave motion) Examples: Sound Waves Seismic waves that travel through the earth Particle motion moves parallel to wave propagation (wave motion) Examples: Light waves Seismic waves that travel on the surface of the earth

Types of Waves Tuesday July 15, 2014Waves5 Use your slinky to model longitudinal and transverse waves

Wave Characteristics Tuesday July 15, 2014Waves6 Wave Cycle Wave cycle Oscillation

Wave Characteristics Tuesday July 15, 2014Waves7 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 Characteristics Period 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, 2014Waves8

Period-Frequency Relationship Tuesday July 15, 2014Waves9

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, 2014Waves10

Wave Characteristics Tuesday July 15, 2014Waves11 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 Relationships Wave-Speed Wavelength (λ) Frequency (f) Propagation speed (v) v = λf Rearrange this equation to solve for wavelength. λ = v/f Example: Sound The speed of sound at 25 °C (about room temperature) is m/s. Assume you are playing the piano and strike middle C (frequency Hz). Calculate the wavelength of middle C. Determine the period of this sound wave. Tuesday July 15, 2014Waves12

Electric Charges The atom Tuesday July 15, 2014Waves13

Electric field lines Tuesday July 15, 2014Waves14

Electromagnetic Waves Tuesday July 15, 2014Waves15 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, 2014Waves16 Check out this simulation on electric fields

Electromagnetic Waves Tuesday July 15, 2014Waves17 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, 2014Waves18 Check out these simulations to relate electric fields to how your CricketSat works. EMWave.swf (this one runs automatically) EMWave.swf (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 10 8 m/s Tuesday July 15, 2014Waves19

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, 2014Waves20 M = Mega = 10 6 = 1 million k = kilo = 10 3 = 1 thousand

EM Spectrum Tuesday July 15, 2014Waves21

Atmospheric Opacity Tuesday July 15, 2014Waves22 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, 2014Waves23 Make a statement about the percentage of visible light in the entire EM Spectrum

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Frequency allocation chart Tuesday July 15, 2014Waves25

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