Attach a pencil lead to a small wooden board, attach a wire to one end, and bend the end of the other wire into a small ring and put it on the pencil lead. This is a simple pencil lead sliding rheostat. Connect it in series in the circuit, move its active end, you can change its resistance value in order to control the current in the circuit.
If you need to change the resistance in a larger range, put a few pencil leads in series with the resistor above (see pic ).
It's much easier to start experiments with rheostat. The commonly used rheostat are a sliding rheostat and a resistance box. A sliding rheostat can gradually change the resistance value but cannot accurately indicate the resistance value. If you need to know the exact value of the resistor that is connected to the circuit, you need a resistor box. Resistors of various values are marked on the resistance box, which is convenient to use.
Rheostat have a wide range of uses, for example, adjusting the volume of a radio, controlling the speed of tram, changing the brightness of a theater light and etc.
Source from: Geekfans
Translated by: Utsource