FOCUS 2 - FEATURES OF THE WAVE MODEL CAN BE USED TO ACCOUNT FOR

THE PROPERTIES OF SOUND

8.2 The World Communicates

Sound Waves

Sound waves are vibrations or oscillations of particles in a medium.

The particles in a sound wave oscillate at the same frequency as the source.

Sound waves can not travel through a vacuum.

13. Identify that sound waves are vibrations or oscillations of particles in a medium

Sound waves require a medium to travel through

In Space no one can hear you scream!

The speed of sound waves depends on the medium. Speed of sound in

Air = 331 ms-1 Water (25oC) = 1498 ms-1 Glass = 5640 ms-1 Aluminium = 6420 ms-1

Speed increases as the density of the medium increases.13. Identify that sound waves are vibrations or oscillations of particles in a medium

Cathode Ray Oscilloscopes (CRO’s)

An oscilloscope is a laboratory instrument commonly used to display and analyse the waveform of electronic signals.

The sound to be analysed is played into a microphone which converts the sound waves into an electrical signal with the same properties as the wave. This signal is displayed on the screen.

14. perform a first-hand investigation and gather information to analyse sound waves from a variety of sources using the Cathode Ray Oscilloscope (CRO) or an alternate computer technology

Representing Sound waves...

15. relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them

Pitch and Volume of Sounds

As frequency increases the pitch of a sound increases.

As the amplitude increases the volume of the sound increases.

Q. Which sound below has the: highest pitch? highest volume?

16. explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

Echoes

Echoes are reflections of sound wavesUsed by some animals in echolocationUsed in SONAR and Ultrasound

17. explain an echo as a reflection of a sound wave

Echoes

Using echoes to find the distance to objects.

For the diagram to the left it takes 5 seconds for the sound waves to travel to the object, be reflected and received back at the source.

The speed of sound in air is 330 ms-1

Using

Distance = 1650 m But this is the total distance

the wave travels (ie. Up and back)

So the distance to the object is 825m17. explain an echo as a reflection of a sound wave

Time = 5 seconds

time

distancespeed

5

distance330

Distance = 1650 m

Distance = 825 m

Echo Point – Blue Mountains

A physics tourist attraction!

17. explain an echo as a reflection of a sound wave

Principle of Superposition

“At any point where two waves overlap or meet, the total disturbance is the sum of the individual disturbances caused by the waves at that point.”

http://www.surendranath.org/Applets.html

18. describe the principle of superposition and compare the resulting waves to the original waves in sound

Constructive Interference

Constructive interference results in an increase in amplitude.

18. describe the principle of superposition and compare the resulting waves to the original waves in sound

Destructive Interference

Destructive interference results in a decreased amplitude, or the waves may even cancel each other out.

18. describe the principle of superposition and compare the resulting waves to the original waves in sound