'And then they bite you...'
Ellen starts her mosquito farm - and then explains to Kate what she intends to do with them. It's all in the call of the wild video extra.
Call of the wild diaries
Jonathan Hare's diary about the challenge for the Call of the Wild programme, from the BBC/OU series Rough Science 5
The idea of this challenge is to make a hydrophone to allow us to hear the sea creatures under the water. A hydrophone is basically a waterproof microphone, instead of picking up sound waves in the air it picks up sound generated pressure waves in the water.
The heart of the solution to making the hydrophone is a wonderful collaboration between the chemist and the physicist. Mike B, our chemist, is making some piezoelectric crystals. These have the property that they generate electricity if pressure is applied to them. If the pressure is high enough quartz crystals can generate 1000s of volts and make a spark. These are to be found in cigarette lighters and gas oven lighters.
The piezoelectric crystals Mike made are softer than quartz and although they will not be able to generate very high voltages they can produce voltages with less pressures. The idea is to take one of the crystals and fix it to a diaphragm. When sound hits the diaphragm from the air or when in the sea, it transfers the sound vibrations into pressure waves in the crystal. These make the crystal generate electricity and we have the basis of a microphone or a hydrophone.
Today I make up a simple amplifier from old radio parts and get the thing working live on camera which was a bit of a eureka moment. Make up a box for the loudspeaker so that it sounds better. Now I have to wait for Mike B to do his magic with the crystals …
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Content last updated: 26/01/2005
