Ammeters and Voltmeters
It is not just enough to know how to connect electrical loads to construct electrical circuits. Learning how to measure the different quantities in a circuit is also important. Aside from using the corresponding equations to calculate the electric current and potential difference (commonly called as voltage), there are also devices used to measure them. These devices are known as the ammeter and voltmeter.
An ammeter is used to measure the current in an electric circuit. It has very low resistance so as to minimize the potential drop through it and to minimize its impact to the circuit.
A voltmeter is used to measure the potential difference between two points. It has very high resistance to minimize the current flow through it and also to minimize its impact to the circuit.
These devices are not just connected anywhere in a circuit. There are proper ways to connect each of these devices in a circuit to have correct measurements and to avoid breaking the circuit.
In order to measure the current, a circuit must be broken to insert the ammeter and connect it in series with the circuit. This connection will allow the electric current to flow through the ammeter and be measured. When a circuit or portion where the ammeter is used in a circuit is opened after removing the ammeter, this indicates that the ammeter is connected correctly to the circuit.
The voltmeter is connected in parallel with the element to be measured. Removing it without breaking the circuit is an indication that it is connected correctly to the circuit.
In a circuit diagram, the symbols used to denote ammeter and voltmeter are shown in the figures below.
Below is an electric circuit diagram with a voltmeter and ammeter correctly connected to it.