Testing your mettle
Mike's got a spot of trouble - he's suffering from the corrosive effects of seawater. But he's got a plan, as you can find out in the reef video extra.
The reef diaries
Jonathan Hare's diary about the challenge for the Reef programme, from the BBC/OU series Rough Science 5
For this last programme [next week's challenge was filmed earlier - editor's note] we decide to build a burglar alarm for a reef!
The idea is to suspend an insulated wire above the water in front of a reef. If a boat comes too near and touches this ‘tripwire’ its wet bow will electrically connect the wire to the sea. An electrical circuit will detect this ‘boat made circuit’ and trigger an alarm - that’s the plan. The apparatus has to be powered by the sun and from the waves to be self-sufficient and ecologically sound!
The Rough Science team all get together to plan. Mike, Kathy and Ellen are to make a string of flags and floats which will form the fence on which to hang the ‘tripwire’. I will work on converting a household smoke detector so that it can be triggered by the tripwire and boat. I also am really looking forward to making a wave powered generator - something I’ve wanted to do for years but never (for some reason!) wanted to do in the wet and cold of Brighton beach. Now I can do it out in the heat and sunshine of the Zanzibar sea!
I set up a little demo to show Kate how electricity can be generated from a coil of wire and a magnet – I show her the shake-a-gen. Talk to her about how I will modify this to make the wave powered generator. This works by using waves (or swell) to rock magnets in and out of wire coils so generating pulses of electricity. There is a long metal ruler in the Rough Science kit which I decided to use for the flexible support for the moving magnets. It also has the convenience that the magnets stick to it.
I make up two coils for the wave generator of about 1000 turns each and mount them so that the rocking magnets fall into one and then the other coil. I then make up two rectifiers and capacitor storage devices from the radio parts that will smooth the pulsed power so that (like a battery) it will power the smoke detector electronics properly. It will also allow me to add the voltages together to get enough to run the smoke alarm.
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Content last updated: 26/01/2005
