I still have a very vivid memory of being in the wonderful old tiled room working on the makeshift bench. Every so often I would look out of the glassless window across the deep blue mediterranean, out over to mainland Italy. Sun light was casting bright optimistic rays onto the bench and as I watched-on very awake, a camera somehow formed by itself out of bits of wood in front of me. It was one of those moments when you stop worrying about things, are able to concentrate at whatever is at hand and really enjoy the moments.
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How to make a sea water battery
There are some magic moments in science when you feel like you have got something for nothing. One example of this is the crystal set radio that not only picks up signals from far away but does so without a battery ! (it gets its power to drive the earpiece from the radio wave energy). Another nice example is the sea water battery we 'knocked together' on the second Rough Science TV programme.
It has been know for hundreds of years that if two different metals (conductors called electrodes) are placed in a liquid a voltage will be produced between them. The metals need to be quite different from each other, for example lead and zinc or carbon can also be used. Carbon is the 'lead' or graphite in pencils and so is easily found. The liquid needs to be what is called an electrolyte, which is basically a water solution having a chemical dissolved in it. The chemical is often an acid but other compounds can be used - even salt (sea water).
For our first try at making a battery Mike, Kate and I found an aluminum jug which we filled with sea water. We thought at first that we could wire straight onto the jug but later we used a zinc plated bolt to make sure the connection was good. A pencil lead (graphite) was used as the other electrode with a wire attached to it for the other connection. Aluminium reacts very fast and forms an oxide coating all over it, hence it probably wasnt very good for a battery because although it might have produced quite a lot of electricity at first, it probably would have stop quickly. In reality the zinc bolt probably acted as the second electrode.
A row of sea water batteries - our 'ocean power plant' !!
This very crude battery made-up out of a jug, zinc bolt, pencil and sea water was our first attempt at making electricity and it worked !! Later on I made one of these at home and found that it could give between 0.7-1 volt and, flat-out supply perhaps 10 milli amps (about 1/100 Watt power).
Feeble as this is, it was enough for our compass experiment. Here we took a needle and tried to magnetise it using the electricity from the sea water battery. To make a magnetic field from electricity all you need to do is pass the elctricity through a coil of wire which produced the magnetic field within it. If the needle is place in the coil it becomes magnetised over time.
We wound several hundred turns of fine wire around a makeshift cardboard former (about 3cm long and 0.5 cm diameter). We made some iron fillings by filling up a nail and tested our needle to see that it was not already magnetised in some way. We found that the needle did not pick up any of the filings when brought near it, which confirmed that it was not magnetised.
We then placed the needle into the coil and wired it up to the battery and left it for a few minuets. Then we brought the needle (still within the coil) near to the iron filings and as if by magic it picked up the fillings - our sea water battery and coil had magnetsied our needle !! This needle was then floated on water (on a leaf) and the magnetised needle slowly turned round to align with the Earths magnetic field. The Earths Magnetic field is a curious thing as it is at once both feeble and giant! Feeble as it is its interaction with the magnetised needle produces a force strong enough to pull it round and align it - our compass worked.
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How to make a meter
In order to test out our sea water batteries we devised a simple (well sort of simple) meter. Its one of my only regrets about the TV work, that on leaving the Island I didnt take the meter back home with me. We had a lot to do at the end of the programmes and, what with everything, I forgot the meter.
This was one of those lovely experiments done for fun and it just about worked! Four coils of wire were made up (about 500 turns 2cm diameter). Three were all wound clockwise while one was wound anticlock wise. I made up a simple see saw (a piece of thin wood 3cm x 25 cm) that rested on a heavy wooden base. The see-saw was balanced on two washers fixed to the wooden base. This was done using two fine nails fixed to the centre of the see-saw. Also at the centre of the see-saw was fixed a pencil that would form the pointer of the meter. Below this was fixed a small collection of nuts to counter balance the weight of the pointer.
One of the 'clock wise' coils was fixed to one end of the sea-saw and to the other end was fixed the anticlockwise coil. Underneath each end of the see-saw, about 1cm below the coils on the wooden base, were fixed the two other clock wise coils of wire. The coils were carefully wired up so that the current would flow through all the coils the same way appart from the anticlockwise coil which would flow the other way.
When a current was passed through the set-up (ie. when testing the batteries) a magnetic field is created in each coil. For example, the top of one of the coils may become the north pole while the bottom will become the south pole. The four coils therefore each act as seperate magnets. One end of the see-saw has two coils wound the same way and so if the top, of the top, coil becomes 'north' so will the top of the underneath coil. Meanwhile the bottom of the top coil has become south (are you still following me!). The bottom and top coil therefore see opposite magnetic signs and tend to attract one another. The other end of the see-saw has two coils wound opposite to each other and so by a similar argument these two will always repel each other. If one end of the see-saw is attracted to the base while the other end is repelled the see-saw will tend to move in one direction. This will move the pencil pointer and 'hay presto' you have an indication of the current passing in the circuit - you have a current meter!
The see-saw is a bit insensitive! It would have been far better to use two strong magnets on the base and two coils on the see-saw but there you are, one always knows best with hindsight. However there are some advantages to the meter. Firstly it does not matter which way the current is flowing. So the meter will always read the same way. This means that the meter will work just as well with AC or DC current.
Please, Please, if you have a go at making this meter do not, DO NOT use it on the mains electricity - no never, please dont do that ..
It is virtualy impossible to get the see-saw to balance on its own. I made up a very simple spring of about five turns using a piece of fine wire wound around a pencil. This was fixed to the base and onto the see-saw (about a 1/3 of the way along from the center pivot) and adjusted so that the see-saw was midway - i.e. the pointer was straight-up with no current flowing. By fiddling around with finer and finer springs one can get the meter to be more and more sensitive to current (but also unfortunately sensitive to wind etc.). Also using more turns of wire on the four coils will improve sensitivity. I dont think this meter could detect currents much less than about 1/20 amp. In our 'ocean power plant' we wired up ten sea water battaries (two lots of five in parellel wired these two sets then wired in series) to increase the power (voltage and current).
Mike and Vanessa watching over the electrolysis to make silver iodide
The silver iodide produced in this simple apparatus forms yellow/green crystals that fall out of solution. However it is sparingly solouble in water, and almost colourless, so by dipping a piece of paper into the solution we can coat it in silver iodide. Silver iodide is sensitive to light which decomposes to form a dark silver (or silver oxide) compound that is easily seen.
A piece of paper dipped into the solution and left in the light will darken over time (in about half an hour in bright sunlight, depending on the strength of the solution). If the paper is partly covered by a key, for example, after a little while a negative image of the key forms on the paper. That was the basis of the photographic film used in our camera - amazing when you think it started life as seaweed!
Vanessa and Jonathan - out on location with the camera and homemade tripod
The Camera was a simple wooden box having a hole in the top. Over the hole was placed a piece of the bottom of a glass bottle found on one of the many tips near the prision 'laboratory'. One of these glass 'lenses' actually worked. Mirrors and a simple screen were made up so that we could focus an image onto the photographic paper via the simple lens. As you saw on the TV programme, although in principle the idea was sound, there were large technical problems to be overcome to get the camera and film to work really well. However we showed that it might be possible given a lot more time (and sunshine!).
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(all photos: Jonathan Hare)
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