Waves And Wave Properties Applied Physics and Chemistry SHM Lecture 2

Wave  A disturbance that transmits energy  Mechanical waves: require a medium to move  Transverse waves  Longitudinal waves

Transverse Wave  Movement perpendicular to direction of wave  Example: light

Longitudinal Wave  Movement parallel to direction of wave  Series of compressions and rarefactions  Example: sound

Measuring the Wave  Speed: depends on the medium  Measured in m/s  Amplitude: maximum displacement from rest  Wavelength: distance between points where wave pattern repeats  Frequency: number of waves that pass a point in one second  Measured in Hertz (Hz): 1 Hz is one wave/second

Wave Equation   Relates frequency, velocity and wavelength V = f λ  There is also a relationship between period and frequency  T = 1/f

Sample Problem  A sound wave has a frequency of 192 Hz and travels the length of a football field (91.4 m) in 0.271 s. What is the speed of the wave?

  Known: f=192 Hz d=91.4 m t=0.271 s Equation: V=d/t (no known λ)  Solve: V=(91.4m)/(0.271 s) = 337 m/s

Sample Problem Continued  Find the wavelength of the wave.

    Known: V=337 m/s f=192 Hz Equation V=f λ so λ=V/f Solve: λ=(337 m/s)/192 Hz So λ= 1.76 m

Sample Problem Continued  What is the period of the wave?

 Known: f=192 Hz  Equation: T=1/f  Solve: T=1/192 Hz  T=0.00521 s

Sample Problem Continued  If the frequency was changed to 442 Hz, what would the new wavelength be?

    Known: V=337 m/s f=442 Hz Equation: V=f λ so λ=V/f Solve: λ=(337 m/s)/(442 Hz) And λ=0.762 m

Now you try it!

 Solve the problems on your worksheet! Remember the wave equation and the relationship between period and frequency.