WaveNature of Sound

Reflection, refraction, diffraction


Toothed whales (a group that includes dolphins), bats, and some shrews use ecolocation to navigate their surroundings. Each of these animals emits high-frequency sound pulses and, in turn, detects the echoes produced by those sounds. Special ear and brain adaptations enable them to build a three-dimensional picture of their surroundings, much like radar. Bats, for example, have enlarged ear flaps that gather and direct sound towards thin, supersensitive eardrums.

Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. These frequencies are between 1 MHz and 10 MHz (mega, M, is one million or × 106) and such frequencies cannot be heard by humans

The technique is similar to the method of location used by bats, whales and dolphins, as well as SONAR used by submarines. (SONAR stands for Sound Navigation and Ranging)

Ultrasound is a ‘non-invasive’ imaging method with instant results, relatively inexpensive, with little or no health risks

Doppler ultrasound can be use to view blood flow through the heart and diagnose circulation problems


lesson 2

Reflection, refraction, diffraction, interference.

Speed of sound in various media.


lesson 3

speed of sound is slower than light.

Speed of Sound in Air - Bang and Time Method

Posted in Physics by esfscience on April 1, 2009

How it’s done…

1. Find a field with a wall, or a tall, wide building at one end of it. The school car park will work fine - there’s a brick wall at the North end which reflects the sound back to the experimenters very well.

2. Pace out 100m from the wall. Thank you, ladies.

3. Bang two wooden blocks together sharply and listen for the echo. It sounds like the crack of a cricket ball being struck.

4. Bang the blocks together again at exactly the same time as you hear the echo You might have to practise this to get it exactly right.

5. Start a stopwatch and time how many bangs you make in one minute.

6. Repeat twice more and average for accuracy.


• Number of bangs in 60s = 96 (average of 3 times)

• Time for the sound to travel there and back once = 60/96 s =o.625s

• Distance travelled by the sound waves there and back = 2 x 100m

• Given that : Speed = distance/time, the speed of sound in air = 200m/0.625s = 320m/s.

The actual value is closer to 343 m/s or 1236 km/h, which increases with increasing temperature.

Demonstration of interference, e.g. two loudspeakers and a signal generator.

Demonstration that sound requires a medium.

Set up the apparatus as it is in the diagram, if it is possible to suspend the alarm clock off the base that would be good.

Before you turn on the pump have the alarm clock set to go off, you can hear it only a little more muffled than when it is out in the open.

Turn on the pump, listen to the sound of the alarm now.

If you like you can use a noise meter, and write down the value every 15 seconds.

Set up the apparatus as it is in the diagram, if it is possible to suspend the alarm clock off the base that would be good.


Reduction of noise using destructive interference.

Noise pollution.

Breaking the speed of sound