Electricity: Current and Circuit Symbols

Understanding Current

Electric current refers to the flow of electric charge in a circuit.
It’s measured in amperes (A).
Current flows from the positive (+) side of the cell to the negative (-) side, this is known as conventional current flow.
The two types of current are direct current (DC) and alternating current (AC). DC is a constant current that flows in one direction, whereas AC periodically reverses direction.
Ohm’s law states that the current (I) through a conductor is directly proportional to the voltage (V) across it, provided the temperature remains constant. The formula is I = V/R.

Circuit diagrams use symbols to represent the different components.
A cell is represented by one small and one larger parallel line.
A battery comprises two or more cells, and is represented by multiple pairs of parallel lines.
A flat line or a line with three smaller lines branching off it illustrates a wire.
An arrow pointing to a wire represents current.
A resistor is shown with a jagged line while a variable resistor has an arrow across it.
A lamp is represented by a circle with a cross inside.
A diode is a triangle pointing to a line.
A circle with an ‘A’ inside stands for an ammeter, whereas a circle with a ‘V’ is a voltmeter.
A closed loop is a switch in the closed position and a semi-open loop is a switch in the open position.

The key components of a simple electric circuit are a power source, a load (such as a light bulb or a fan), a switch, and connective wires.
The power source or cell provides the voltage that drives the current around the circuit.
The load provides resistance which controls the flow of current.
The switch allows the current to be turned on or off by opening or closing the circuit.
Connective wires conduct the current from the power source, through the load, and back to the power source.

Identifying and understanding these core topics around electricity will prove valuable for understanding more complex aspects of electrical circuits.