Sound

SoundGCSE Physics

Aims of the lesson

• To recall how a sound wave is created and travels through a medium

• To state how different sounds can be produced and relate this to the frequency and amplitude of the wave

Doppler Effect

Going Super Sonic

Cathode Ray Oscilloscope

Wave Animation

Complete the CRO tracesOriginal

Frequency x2 of OriginalFrequency x2 and ½ amplitude of Original

Exactly the same sound (only a couple of seconds later)

Aims of the lesson

• To recall that sound can bounce off surfaces

• To describe how sound waves can be used to detect objects both in industry and medicine

EchoesEchoes• An echo is a reflected sound.An echo is a reflected sound. When sound

is reflected off a plane (or flat) surface-

• Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection

Some of the energy of the

incident wave will be absorbed

when it is reflected by a

surface.

ExamplExamplee• A fishing boat sends out a pulse of ultra sound. The reflected pulses are detected after 0.8 s and 1.4 s.0.8 s and 1.4 s. The speed of ultrasound in water is 1500 m/s.1500 m/s.

• Calculate 1.) the depth of the sea bed and 2.) the depth of the shoal of fish.

1. Distance x 2 = Speed x Time

= 1500 x 1.40

= 2100m

2. Distance x 2 = Speed x Time

= 1500 x 0.8

= 1200m

The sound travels double the distance

so…

Distance to sea bed = Distance to sea bed = 2100 / 2 = 1050m2100 / 2 = 1050m

Distance to shoal of Distance to shoal of fish = 1200 / 2 = 600mfish = 1200 / 2 = 600m

http://www.radiologyinfo.org/en/info.cfm?pg=genus&bhcp=1

How is ultrasound How is ultrasound used?used?

• Ultrasound (>2000020000 Hz) like all sound is reflected differentreflected different amountsamounts by different materials.

• A receiver can be used to detectdetect the amount of ultrasound reflected or lost from a signal.

• A computer can then be used to build up an imageimage of these ultrasound signals.

• This is how ultrasound is used in prenatalprenatal scanning and industrial quality control.

• How do these animals use sound to aid them?

Page 89 and 90Page 89 and 90

Measuring Speed of sound

The results are in…The results are in…

• Using this set of results, calculate the speed of sound in air-

• The exact speed of sound is 330m/s, what what errors in the experimenterrors in the experiment could account for a lesser value?

Time (s) 0.425 0.462 0.470 0.432 0.447

Attempt 1 2 3 4 5

Distance = 134mDistance = 134m