Waves PHY1014/1024 Physical Science Lecture 9: Waves, Sound, & Light Professor Kenny L. Tapp Waves&are&disturbances&(energy)&that& propagate&(move)& Waves&involve&a&oscilla8on&of&something& about&an&equilibrium&point Pendulum(swinging Block(and(Spring(oscilla5ng Air(Molecules Electric(and(Magne5c(fields Waves A wave pulse is a disturbance that propagates through a medium. It transfers energy without transferring matter; the energy is a combination of kinetic and potential energy. Types&of&Waves Determine&by&the&orienta8on&of&the&par8cles& oscilla8on&to&the&direc8on&of&the&pulse s& mo8on Transverse&wave& &par8cle s&oscilla8on&is& perpendicular&to&the&pulse s&mo8on& Light(waves,(sin(waves,(S(waves(in(earthquakes Longitudinal&wavesA&par8cle s&oscilla8on&is& parallel&to&the&pulse s&mo8on Sound(waves,(P(waves(in(earthquakes Longitudinal Types of Waves Transverse Types&of&Waves Longitudinal Transverse
Waves& Parts( Ocean&water&movement& Crest& Trough Measurements(of(a(wave Wave&height& &the&distance&between&a&trough&and&a& crest& Wavelength& &the&horizontal&distance&between& successive&crests&(or&troughs) Wave&period& &the&8me&interval&for&one&full&wave&to& pass&a&fixed&posi8on&& The&basic&parts&and&movement& of&a&non5breaking&wave. Google s&floa8ng&data¢er Powered&by&waves Reduce&cost&of& ownership&by&50% Parts&of&a&Wave Relationship between wave speed, wavelength, period, and frequency: The company filed a patent application for a "waterbased data center" detailing a floating data center, complete with an energy supply fed by a wavepowered generator system and a wind-powered cooling system using seawater. Wavelength & Frequency Short wavelength High frequency When two or more waves travel through the same medium at the same time, they interfere in a process called superposition. At any time, the combined waveform of two or more interfering waves is given by the sum of the displacements of the individual waves at each point in the medium. Long wavelength Low frequency This is an illustration of interference, using the principle of superposition. The displacement of any point on the rope is the sum of the individual displacements: Wavelength&increases&=&Frequency&decreases
Superposi8onA&Mul8ple&waves&in&a&medium& will&combine&to&for&a&single,&some8mes& complex,&waveform Accomplished&by&interference Construc5ve(interferenceCcombined(waveform(is( greater(in(amplitude(than(the(individual(waves Destruc5ve(interferenceCcombined(waveform(is( reduced(in(amplitude(than(the(individual(waves( If the combined wave is larger than the individual ones, the interference is constructive; if smaller, it is destructive. Destructive interference is used in noise-canceling technology. Sound Waves These pressure waves hit the eardrum and are converted to nerve impulses, which our brains interpret as sound. Sound Waves Ultrasonic waves are too high in frequency for human ears. Dogs, cats, and bats can hear higher frequencies. Infrasonic waves have frequencies too low for human ears. They are produced by earthquakes and other natural phenomena; elephants and cows can hear certain frequencies.
The%Speed%of%Sound The%Speed%of%Sound:%%FIREWORKS Speed of sound in dry air: July 4, 2011 10:05pm Air Temperature (Celsius) Note the dependence on temperature. v = 331 + (0.6T c) = 331 + (0.6)(30) = 349 m/s The%Speed%of%Sound:%%FIREWORKS The%Speed%of%Sound:%%FIREWORKS Determine the distance that Prof. Tapp was watching the fireworks from on July 4, 2011. V sound = d / t Sound%Intensity%and%Sound%Intensity%Level Sound%Intensity%and%Sound%Intensity%Level Intensity&is&perceived&as& loudness&and&is&determined& by&the&litude&of&the& wave Intensity&is&rate&of&energy& transfer&over&an&area Works&like&spray&paint,& decreases&as&a&func8on&of& distance&squared&from&the& source Intensity&can&be&measured&in& decibels We perceive sound intensity as loudness; the minimum detectable sound has an intensity of about 1.0 10 12 W/m 2, and the threshold of pain occurs at an intensity of about 1.0 W/m 2. A doubling of loudness corresponds to an increase in intensity of about a factor of 10. Sound intensity is measured on a logarithmic scale, in decibels:
Sound%Intensity%and%Sound%Intensity%Level Electromagne8c&Spectrum Ultraviolet Infrared Gamma Rays X-rays Visible Radio Wavelength decreasing, Frequency increasing Visible light occupies only a tiny sliver of the full spectrum. Speed of Light Speed of wave, c, equals wavelength times frequency. The speed of light in a vacuum is always c = 300,000 km/s (186,000 miles/sec). ENERGY As a car or train horn approaches you and then passes by, the pitch of the sound first rises and then falls. This is called the Doppler effect.
If an object is moving faster than the speed of sound, it will outpace its sound waves, creating a sonic boom. A similar phenomenon produces the wake from a boat it is going faster than the wave speed in water.