An electric current is the continuous flow of electrons in an electric circuit. As electrons carry a negative electric charge, this means an electric current is a flow of charge.
For an electric current to flow, we need:
When a circuit is complete (closed), the charge will flow around the circuit.
We measure current using an ammeter
Current is measured in amperes, also known as amps or A. The higher the charge, the bigger the current. The circuit symbol for an ammeter is:
Connect the ammeter in series with the component you are measuring in a circuit.
Below you can see a diagram of a circuit with an ammeter and the same circuit using circuit symbols at the bottom. When placing an ammeter in a circuit, it must be placed in series with the circuit, so that the current you are measuring flows through the ammeter.
This includes the cell, the lamp, the switch and the wires connecting to the ammeter.
Let’s look at potential difference.
The potential difference (otherwise known as voltage) is the difference in energy between two components of a circuit. The higher the difference is, the higher the potential difference.
We measure potential difference using a voltmeter.
Below is the circuit symbol for a voltmeter.
Connect the voltmeter parallel with the component you are measuring in a circuit.
To measure the potential difference of a component, you connect a voltmeter with two wires and attach them to either side of the component you are measuring.
In the diagram below, you can see what the circuit would look like if we wanted to measure the potential difference of the lamp.
On the top right is the voltmeter, with the symbol V.
If we wanted to measure the potential difference of the lamp above, we connect a wire to either side of the lamp and then to the voltmeter. If we put the voltmeter in the same loop as the component we are measuring, it will not work.
|Measuring device||Ammeter in series||Voltmeter in parallel|
|Circuit symbol of measuring device|
|Unit||Ampere (A)||Volt (V)|