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An attractive-looking gold-leaf electroscope, charged using a rubber balloon rubbed against people's clothes. The shiny, coiled-wire cage around the gold leaf has an earth lead terminating in a crocodile clip. A wire connects the brass ball to another one on a separate, insulated support. Users are prompted to try charging and discharging the electroscope by means of the second brass ball. In this way they can observe so-called 'static' charge flowing along the wire.
Magnetic forces
Background text :
These experiments show what magnetic forces do. They also reveal a mysterious and important link between magnetic forces and electric currents.
The forces are strong at parts of the magnet called the poles. They are called north poles and south poles because of the direction they face when the magnet is hung from a thin thread.
The north and south poles of magnets attract each other, but two north poles or two south poles push each other apart.
Magnets
Magnetic forces that can be felt as well as seen. Three pairs of hanging magnets show the principles of attraction and repulsion particularly impressively. The pair of pivoted magnets reinforce this, and the hovering ring-magnets ask a question : where are their poles? The tethered, plastic-covered bar magnet rests on a protected array of tiny iron needles, showing the patterns of a magnetic field.
Magnets and wires
Moving a tethered bar magnet and so changing the magnetic forces acting on a wire coil produces a current shown by an ammeter.
The separate experiment on the left shows a converse effect. By using the loose wire to complete a circuit, you pass current through two other coils and produce a magnetic field strong enough to attract a tethered steel disc.
Circuits and currents
Background text :
Here we can see and measure the way charge flows around a circuit.
Voltage is an electrical force which 'pushes' charge and makes it flow. The flow of charge is called an electric current and is measured in amps.
Some substances such as metals, whose charge can easily be made to flow, are called conductors.
Substances whose charge does not flow easily are called insulators. Metal wires with a plastic insulator covering the outside are a useful way to make an electric current flow around a circuit.
Circuits can be designed to control electric currents, so that we can use them to do many useful things.
Is it a conductor?
Two loose leads are used to find out which of the various material samples allow current to pass through. Users are also prompted to search their pockets for more samples to test!
Current is indicated by an ammeter and a buzzer. The arrangement of the circuit and its connection to the power supply are clear and obvious.
Light the lamp
The simple challenge is to figure out how to light the lamp and sound the buzzer, using the three loose leads. It may look too easy but this is soundly based on educational research. The 'naive notion' is that it should light if only one side of the circuit is connected. This is now the fourth time I have produced this kind of experience, and I know for a fact that a high proportion of primary school teachers find it far from obvious!
You can't easily do this by yourself because there are (deliberately) three connections which come apart when you let go and you only have two hands. You have to call a friend over to help. Then you discuss it together.
Deceptively simple-looking, the three loose leads in this clearly laid-out circuit present very many experimental possibilities. The questions on the hanging disc are powerful ones. "How many ways can you find to light two lamps?" "When all lamps are lit, what do you notice about the readings on the three ammeters?" "Is it possible to light three lamps so that they all shine with the same brightness?"
Generating and using 'electricity'
This is another section, unfinished and still in planning. It will be clearly distinguished and have its own exhibit 'clusters'. Meanwhile just three interactives have been produced as part of that future logical arrangement.
Generator
You spin the horseshoe magnet (which really looks like a magnet!) above the wire coil and see the resulting current registered on the ammeter. You can choose to generate alternating current or direct current, depending on whether or not you include the little diode in the circuit which you complete using the loose lead. This seems particularly relevant for a power station visitor centre.
Make a motor
You take a length of polyurethane-coated copper wire, follow the instructions to form it into a simple coil, then remove the insulating coating from one end using the file. At the other end you just remove the coating from one side of the wire, at right angles to the axis of the coil (users get this from the diagram, not just words!). Next, you carefully balance your creation on the two metal hooks, above the magnet, and watch it spin gaily as current flows through it.
(Any unscrupulous designer trying to pinch this idea from me should beware of burning visitors. My prototypes produced showers of sparks or became spectacularly hot when a coil was left to rock gently and arc. Since these interactives were to be 'launched' by a participative royal visit from the Queen, I had to concentrate pretty hard on making this one safe!)
Visitors too young or too impatient to succeed with the challenge of making the coil spin can use the loose lead to operate a selection of 'proper' electric motors.
Electronic circuits
A circuit board programmed to show some of the things that more complex circuits can do. Touching one of the screw-heads with a loose lead switches on an electric motor. Successive touches of the same screw-head stop the motor, change its speed, then reverse it. The other effects involve an array of light-emitting diodes. Each contact made at one of these connections lights the next LED in a row. Another produces a sequence of LED patterns which more knowledgable visitors may recognise as a binary counting series. The fourth contact shows a 'monostable' state : a red LED simply switches off when that screw-head is touched by the loose lead. After several seconds it switches on again, whether the contact is broken, or steadily held.
The four separate loose leads allow several users to experiment together, demonstrating that these functions can all work at the same time.
Power supply unit etc.
This project required enough flexibility for interactives to be moved and repositioned easily. Providing a power supply for such an exhibit set is not entirely straightforward. Each interactive unit has its own separate voltage and overload protection requirements. Using highly flexible multicore cables and suitable connectors made it possible to meet the special needs of each unit. Small, additional 'extension boxes' were fitted with extra sockets and independant protection devices, so that problems with one interactive unit need not affect any of the others.
The queen has her hands too full to interact!
