Ammeters & Voltmeters

The main feature of an element in an electric circuit such as a resistor, capacitor or inductor is the relationship between the potential difference V across the element and the current I in the element. The simple relationship of un element is Ohm's law for a resistor of resistance R: V = RI. The quatities V and I can be measured by instruments. Current is measured with an Ammeter, and potential difference with a Voltmeter. The ammeter is a device that measures currents in Amperes (A), the voltmeter a device that measures voltages in Volts (V).

1. Ammeters

To measure the current in a circuit element, an ammeter must be placed in series with the element. An ammeter measures the current in itself. The current in the ammeter and in the element are the same.

The galvanometer is an ammeter with high sensitivity.

2. Voltmeters

To measure the potential difference across an element in a circuit, a voltmeter must be placed in parallel with this element. A voltmeter measures the potential difference across itself. The potential difference across the element and across in the voltmeter are the same.