Ammeter

An ammeter measures electric current I in amperes (A); 1 A is 1,000 mA. It connects in series: open the current path and insert the meter so the current flows through it. Its internal resistance is low; an ideal ammeter has zero resistance and no voltage drop. On this center-zero analog meter, swapping the probes reverses the sign and needle direction, not the actual direction of current in the circuit.

Use COM and the appropriate A or mA input on an instrument with measurement sockets. Choose DC current and a suitable range. Never connect an ammeter directly across a power source: its low resistance would create a short circuit.

At SparkVille’s theatre, the crew tests a revolving stage. When heavy scenery is added, the motor needs more current and the ammeter’s needle moves farther. Even a fairy-tale castle made of scenery can give a motor quite a workout!