Ann Marie Wong, age 10, of St. Catharines, Ontario, for her question:
What is a galvanometer?
The word "galvanic" belongs to electricity and a meter is a measurer. A galvanometer is a clever gadget for measuring the strength of electric current. However, electricity comes in AC and DC and each type behaves in its own tricky way. So to cope with these and other problems, the plain old galvanometer comes in different styles for different duties. A certain ammeter style shows its face on the dashboard to tell whether the car's battery is behaving itself.
As we know, toasters and radios, driers and dozens of other everyday items use electricity to do their work. Those than run on batteries use DC, or direct current that runs in the same direction. Those that plug into wall sockets use AC from the power lines. This alternating current jogs back and forth as it goes. But an expert tester needs to know far more details about gadgets that use both AC and DC. Ammeters, milliammeters and micrommeters show the current strength in exact, degree units.
Voltmeters show the pushing volt units in a current. Wattmeters show how many watt units are being used by the moment. The simple galvanometer is the grand daddy of these specialists. Most of them use it with a few extras and slight changes to perform special duties and each takes a special name for itself.
The galvanometer family works because electricity and magnetism are related. Every electric current surrounds itself with a magnetic field that behaves somewhat like the field around a solid magnet. The opposite poles of a small magnet feel this when they are near an electric current. Sealed inside a galvanometer there is a small permanent magnet that senses a weak or strong field around a weak or strong electric current. Several items are linked up to make the galvanometer's magnet reveal what it knows.
Its little magnet is a coil of wire, pivoted on a swinging bar. This is attached to a needle that moves with the magnet and swings its finger across the dial. The two ends of the wire coil form two springs that act as opposite magnetic poles. When they sense a nearby magnetic field, each spring moves up or down. This makes the pivoting magnet move and swing the needle across the face of the dial.
The magnetic field around a busy battery makes a galvanometer swing way over from side to side. This shows that the battery has plenty of stored electricity to perform its duties. But if there is no outside magnetic field in the neighborhood, the needle refuses to budge from the center of the dial. This means there is no electric power either and that poor old battery is dead.