Waves disturbances but in a good way Mostly

Waves disturbances (but in a good way! Mostly )

Definition Waves are disturbances that transfer energy! Tuesday July 15, 2014 Waves 2

Types of Waves Mechanical Waves Electromagnetic Waves • A mechanical wave is a disturbance that propagates through a medium. • A medium is any material (matter) through which a wave travels. • 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. Mechanical wave examples: sound; water waves; a pulse traveling on a spring; earthquakes; a “people wave” in a football stadium. Tuesday July 15, 2014 Waves 3

Types of Mechanical Waves Longitudinal Transverse Particle motion moves perpendicular to the direction of wave propagation (wave motion) Particle motion moves parallel to wave propagation (wave motion) Examples: Sound Waves Seismic waves that travel through the earth Examples: Light waves Seismic waves that travel on the surface of the earth Tuesday July 15, 2014 Waves 4

Types of Waves Use your slinky to model longitudinal and transverse waves Tuesday July 15, 2014 Waves 5

Wave Characteristics Wave Cycle Wave cycle Oscillation Tuesday July 15, 2014 Waves 6

Wave Characteristics • 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!) Tuesday July 15, 2014 Waves 7

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. T = 1/f (the number of waves that occur in 1 second) 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 • 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. Tuesday July 15, 2014 Waves 11

Wave Relationships Wave-Speed • Wavelength (λ) • Frequency (f) • Propagation speed (v) v = λf 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). Rearrange this equation to solve • Calculate the wavelength of middle C. for wavelength. • Determine the period of this sound wave. λ = v/f 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 Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields. Tuesday July 15, 2014 Waves 15

E field simulation Check out this simulation on electric fields https: //phet. colorado. edu/en/simulation/charges-and-fields Tuesday July 15, 2014 Waves 16

Electromagnetic Waves Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields. Tuesday July 15, 2014 Waves 17

EM Transmission Check out these simulations to relate electric fields to how your Cricket. Sat 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) Tuesday July 15, 2014 Waves 18

Speed of Light (c) c = 3 x 108 m/s 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? Tuesday July 15, 2014 Waves 19

Your Cricket. Sat • Calculate the wavelength of the radio wave that your 433 MHz transmitter is transmitting. • Assuming that your Cricket. Sat makes it to 5 km in altitude – determine the time required for the 433 MHz signal to reach your ground station. M = Mega = 106 = 1 million k = kilo = 103 = 1 thousand Tuesday July 15, 2014 Waves 20

EM Spectrum Tuesday July 15, 2014 Waves 21

Atmospheric Opacity Where do the radio waves transmitted by our radio fall into this picture? Do we need to worry about atmospheric absorption? Tuesday July 15, 2014 Waves 22