2 What is a Wave? Watch the two waves. What do you see? How do the particles move?The particles oscillate - they are NOT carried across the screen by the page.KEY POINT: Waves carry ENERGY not MATTERTransverse waveLongitudinal wave
3 What is a Wave? Definition: A wave is a disturbance that carries energy through matter or space without transferring matter.The energy carried by a wave can be substantial – think of earthquakes, tsunamis, or the heat and light of the sun.Transverse waveAs you see here, there are two basic types of waves – transverse and longitudinal.Longitudinal wave
4 Transverse waveThe particles of the medium oscillate perpendicular to the direction of energy transfer/propagation of the wave.Examples:earthquake secondary waves,waves on a stringed musical instrumentwaves on the rope,EM waves: light, radio waves, microwaves…
5 Longitudinal waveThe particles of the medium oscillate parallel to the direction of energy transfer/propagation of the wave.Creates areas of increased and decreased densityAreas of high density / pressure = compressionAreas of low density / pressure = rarefactionExamplesSound wavesEarthquake p wavesCompression in a springTransverse and longitudinal aren’t the only types – there are also surface waves (found on surface of ocean) where particles move in circular pattern
6 Wave characteristics Wavelength (λ) Phase The length of one complete wave cycle of a wavemeasured in metersPhaseTwo points on a wave that occur in the same position within the wave cycle – that is, they are one or more whole wavelengths apart -- are said to in phase.Points in a wave medium can be anywhere from 0° to 360° out of phase with each other.A trough and a crest are 180° out of phase with each other.
7 Wave characteristics Amplitude, A position. ● measured in m ● the maximum displacement of a particle from its equilibriumposition.● measured in m● the greater the amplitude, the greater the energy of the wave● if a wave doesn’t lose energy, then its amplitude remainsconstant; if the wave does lose energy then the amplitudedecreases over time (damping)
8 Wave characteristics Period, T Frequency, f ● is the time taken for one complete wave to pass any given point.● measured in secondsFrequency, f● is the number of waves passing any given point per second.● measured in cycles per seconds or Hz
9 Wave characteristics Wave speed, v Speed of sound in: ● The speed at which wavefronts pass a stationary observer.● Depends only on the medium through which a wave travels!Waves travel faster through material that is stiffer and through material that is less dense.Speed of sound in:air: 343 m/shelium: 1005 m/swater: 1500 m/sbone: 3000 m/ssteel rod: 5000 m/sglass: 4500 m/sSpeaking of medium …
10 Mechanical vs. EM wavesMechanical Waves● Only propagate (transmit energy) through a medium● Make the particles of the medium oscillate at frequency of thewaveExamples: waves on a string, sound waves, earthquakes, etc.,EM (electromagnetic) waves● Can propagate through a vacuum –or- through a medium● Do not cause the particles of the medium to oscillate● Made up of changing electric and magnetic fields● always occur as transverse waves● In a vacuum, EM waves travel at the speed of lightc ≈ 3 x 108 m/s(EM waves travel more slowly through a medium)Speaking of medium …Will talk more about EM waves later!
11 Wave equationA wave generator was used to generate waves of different frequencies in a rope. Two different tensions of rope where used. The wave speed and wavelength were measured.Use the data in the table to answer the following questionsWhich variable(s) affected wave speed?How are wavelength, frequency, and speed related?Only tension (changing the stiffness of the medium) affects speed.λ = (v/f)where,λ = wavelength, mv = wave speed, m/sf = frequency, Hertz (Hz)
12 Check your Understanding Show:A arrives firstB arrives firstSame timeImpossible to determineWave speed depends only on the medium!
13 Check your Understanding c) Wave speed depends only on the medium!
15 You doA sound wave has a frequency of 192 Hz and travels the length of a football field, 91.4 m, in s.What is the speed of the wave?What is the wavelength of the wave?What is the period of the wave?If the frequency were changed to 442 Hz, what would be the new wavelength and period?v = x/t = 337 m/sλ = v/f = 1.76 mT = 1/f = sλ = v/f = m; T = 1/f = sv = x/t = 337 m/sλ = v/f = 1.76 mT = 1/f = sλ = v/f = m; T = 1/f = s
16 You doA sound wave produced by a clock chime is heard 515 m away 1.5 s later.What is the speed of sound in the air there?(b) The sound wave has a frequency of 436 Hz. What is the period of the wave?(c) What is the wave's wavelength?v = x/t = 337 m/sλ = v/f = 1.76 mT = 1/f = sλ = v/f = m; T = 1/f = s
17 You doA hiker shouts toward a vertical cliff 465 m away. The echo is heard 2.75 s later.What is the speed of sound in air there?The wavelength of the sound is 0.75 m. What is the frequency of the wave?(c) What is its period?v = x/t = 337 m/sλ = v/f = 1.76 mT = 1/f = sλ = v/f = m; T = 1/f = s