Despite current is the flow of electrons (negative) through a conducting medium to positive charged atoms, current flow is often or normally defined as Conventional current, where it flows from positive terminal to the negative. In this guide, we will be referencing Conventional current as current.
Current can only flow when there is an energy source that produces voltage. Without this energy source, electrons move randomly and fairly evenly within a wire, and current cannot flow. Energey source creates pressure that drives electrons in a single direction thus creating current flow.
With just energy source alone is not enough to make current flows. The circuit with combination of the energy source (in our example is AA batteries) and load (in our example light bulb) must form a closed loop, a conducting loop which electrons can flow, providing energy to the load connected to the circuit.
The unit for electric current is Ampere (amp) with a unit symbol of A. When working with formula, the symbol for current is I.
Formula, I = V ÷ R ( Current = Voltage ÷ Resistance) - Ohm’s law.
How to Measure Current
Set the multimeter’s knob to the highest possible current setting first, and also make sure that the current fuse rating of the multimeter is high enough to support the current you wish to measure. In the above example, the rough estimated current is only a few milliamp (1 milliamp is 1/1000 amp) based on Ohm’s law, 3V ÷ 1000 Ohm ( 2 x 1.5V battery ÷ 1000 Ohm resistor). Therefore, setting the knob to 200mA setting is a good start point.
In order to measure the current, we need to break the circuit’s loop and let the current flow into the multimeter. The above example shows current flow from the batteries passing through the 1K (1000 Ohm) resistor and into the multimeter then back to the negative terminal of the bottom battery. This forms a closed loop. The reading is 0.003A = 3 mA.
I = V ÷ R
I = 3V ÷ 1000Ω
I = 0.003A