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Waves

Waves. A disturbance in a medium that transfers energy and momentum. To produce a Wave:. A vibration (disturbance) A medium – a substance to travel through. Examples of Waves. Sound Light Water. There are two types of waves.

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Waves

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  1. Waves A disturbance in a medium that transfers energy and momentum

  2. To produce a Wave: • A vibration (disturbance) • A medium – a substance to travel through.

  3. Examples of Waves • Sound • Light • Water

  4. There are two types of waves

  5. Transverse – the individual wave particles move perpendicular to the velocity of the wave. Examples: Electromagnetic waves (light waves, radio waves, microwaves, x-rays) Wave on a string

  6. Longitudinal – the individual wave particles move parallel to the velocity of the wave. Examples: Sound Waves

  7. Wavelength Amplitude Parts of a wave: Frequency – The number of wave cycles in 1 second. Units 1/s = Hertz (Hz)

  8. Wave Interference – The combination of two or more waves. • Constructive interference – Two waves combine to make a bigger wave. • Destructive interference – Two waves combine to make a smaller wave.

  9. velocity wavelength = (velocity)(Period) wavelength (m) Period (s) wavelength (m) frequency (hz)

  10. The Wave Equation v = velocity of the wave (m/s) λ = wavelength (m) f = frequency (1/s = Hz)

  11. Example1: A sound wave has a frequency of 256 Hz. What is the wavelength? The speed of sound is 340m/s.

  12. Example 2: A radio wave has a frequency of 96.9MHz. What is the wavelength? The speed of light is 3.0 x 108 m/s.

  13. Standing Waves on a String The velocity of a wave on the string depends on the mass per length of the string and the tension in the string. v = velocity of the wave (m/s) FT= Tension in the string (N) m = mass of the string (kg) L = length of the string (m)

  14. L The fundamental frequency 1st Harmonic.

  15. The fundamental frequency 2nd Harmonic. L

  16. The fundamental frequency 3rd Harmonic. L

  17. The fundamental frequency 4th Harmonic. L

  18. The fundamental frequency 5th Harmonic. L

  19. Summary fn=nf1 fn= nth harmonic n = 1, 2 ,3, ….. f1 =1st harmonic (fundamental frequency)

  20. L1 P L2 Conditions for interference δ = path difference = L2 – L1 Constructive Interference δ = 0, λ, 2λ, 3λ ……. δ = nλ n = 0, 1, 2, 3, … Destructive Interference δ = λ/2, 3λ/2, 5λ/2 ……. δ = (n+ ½)λ n = 0, 1, 2, 3, ….…

  21. Sound Waves • The speed of sound in air at room temperature is 340m/s. • The speed of sound increases with increasing temperature. • The speed of sound in water is 1500m/s. • The speed of sound in aluminum is 5100m/s.

  22. Physics HumanPerception Pitch frequency loudness Intensity/Amplitude

  23. Pressure fluctuations in air due to a vibrating tuning fork. Applet

  24. Frequency range of the human ear.

  25. Ultra Sound

  26. Human Ear

  27. Sound intensity and the decibel scale

  28. Beats • Beats occur when two sound waves have slightly different frequencies interfere with one another. • The number of beats per second is called the beat frequency. • The beat frequency is determined by subtracting the two frequencies.

  29. Standing Sound Waves in a Tube • The wave travels at the speed of sound (340m/s) • Open ends must have an antinode • Closed ends must have a node. • A pressure wave is set up in the tube. • A tube open at both ends acts just like the string. • A tube closed at one end only has odd harmonics.

  30. Open Tube Just like the string

  31. Closed Tube Odd Harmonics

  32. Resonance occurs when the driving frequency matches the natural frequency, resulting in large amplitude vibrations. Here are some examples of resonance • Pushing someone on a swing. • The Tacoma Narrows bridge. • Breaking a wine glass with a sound wave • Earthquakes totally destroying some buildings and not damaging others.

  33. The Doppler Effect is a change in frequency (pitch) due to the relative motion of the sound source and observer. • As the sound and listener approach each other the frequency is higher. • As the sound and listener move away from each other the frequency is lower. • The Doppler effect also occurs with light producing the red and green shift of distant stars. • Doppler radar is used to track weather systems

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