Experiment 2 - The Current Measurement

But how do you measure the current in a circuit?

If you want to measure current directly, the ammeter needs to be fitted into the circuit ...

Circuit diagram with ammeter for current measurement.

Circuit with ammeter for current measurement. (Enlarge)

The current now flows through the ammeter. This is a direct consequence of the Kirchhoff current law (KCL). The value of current in ampere [A] you read now directly from the ammeter.

But pay attention to two points...

• To insert the ammeter, the circuit must be opened up!
• In an ideal measurement the ammeter does not affects the result...

                 

Ideal Ammeter An ideal ammeter has no internal resistance (Ri = 0 Ω). The current can flow unhindered through the meter and therefore has no influence on the measurement result.

An ideal ammeter is unrealistic. But what is a real ammeter and what influence does it have...?