Sound waves

Introduction

Lessons

  1. Sound waves
  2. Introduction to Sound waves
  3. Variables affecting sound waves

Examples

Lessons

  1. Sound produced by clapping hands is echoed from a distant building 0.4s later, how far is the building? (speed of sound 343m/s at 20°C)
    1. What happens to the wavelength and frequency of sound waves if temperature increases?
      1. Find the wavelength of a sound wave moving in air with frequency of 415 Hz.
        1. The sound detected by human ear is between 20Hz and 20kHz. Find the corresponding wavelengths that can be detected by human.
          1. What physical characteristics of sound is used to decrease the pitch? To increase the loudness?
            1. Sketch a graph of displacement vs. time to represent sound waves, for two cycles of 12-kHz and two cycles of 24-kHz.
              1. If you hear an ambulance siren dropping while passing you, can tell in which direction is moving?

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                Topic Basics

                In this lesson, we will learn:

                • The nature of sound waves
                • How to solve problems relating frequency, wavelength, velocity, pitch, and loudness.
                • Physical properties of sound
                • Doppler shift and applications

                Notes:

                • Sound is produce by vibration of molecules.
                • As the result of collision of molecules, the pressure is transmitted away form the source.
                • Amplitude of sound is the measure of the variation in pressure, in other words Loudness, the louder sound has higher amplitude and more energy.
                • The amplitude is measured by a scale called Sound Level.
                • Sound level is measured in decibels (dB).
                • Pitch:the sensation of frequency, high pitch high frequency.

                Sound waves

                • Speed of sound wave changes upon change in temperature, the higher the temperature the higher the speed.
                • Sound can travel through solids, liquids and gases. (Highest speed in solids)
                • Sound can NOT travel through vacuum (No particles to move and collide).
                • Sound waves are characterized as longitudinal waves.
                • Echoes: Reflected sound waves.
                • Doppler shift: due to motion of the sound source or the observer, the detected frequency changes. The frequency of the source does NOT change.