Outcomes

Pupils can recall the hearing range of a human (20-20,000Hz) and determine whether a frequency lies within the range
Pupils understand that any sound wave with a frequency greater than 20kHz is known as ultrasound.
Pupils can explain the idea of ultrasound scanning using an echo.
Pupils can describe how to measure the speed of sound using a clapping method and an electronic method.

Specification References

3.5 recall and use the relationship between the speed, frequency and wavelength of a wave:

wave speed = frequency × wavelength v = f × λ

time period =1/frequency

3.26 recall that sound waves are longitudinal waves which can be reflected, refracted (and diffracted SA only)
3.27 recall that the frequency range for human hearing is 20 Hz – 20 000 Hz
3.28 describe how to measure the speed of sound in air

Carry out pupil hearing range experiment using speaker and signal generator. Pupils will probably bring up the The Mosquito at this point.

Move onto reviewing (or starting) the two equations needed for this section (v=fλ and T=1/f) you may just quicly want to flag up the regular speed equation (s=d/t) as they often forget that this applies too.
Demonstrate nature of sound waves. AGR has great videos.
- There are lots of animations here
- Show pupils the speed of sound in solids, liquids and gases (set a large value for distance (≈50000m)).
Demonstrate how to find the speed of sound using the "clapper" method.
Demonstrate that sound waves cannot travel through a vacuum.
Pupils will probably ask about shattering a glass with sound.
Discuss the nature of ultrasonic sound.
Discuss the uses of ultrasound in diagnostic sonography, therapeutic medicine, industrial nondestructive testing and cleaning. Why not bring in some jewellery and clean it in the lesson. - Note uses ultrasound is not on the IGCSE syllabus but can still be discussed.

The main risk is from the vacuum pump and apparatus. The specific risk assessment must be read before using the apparatus.