Voltage and Current Basics

This tutorial sets out to explain how voltage and current work in simple terms. At this level of explanation, some technicalities are avoided until later topics.

Electricity

Electricity is the action of negatively charged energy particles known as electrons flowing through a conductor like a wire creating an electrical circuit. We may think of electricity flowing through a wire, into a lightbulb.

A conductor is a material that allows electrons to flow easily through it, with the opposite being an insulator that makes it difficult for electrons to flow through it. Wood and plastics are good insulators, whereas metals such as copper and aluminium are good conductors.

What is Current?

Components that make up an electrical circuit use the flowing electrons to do work, for example, in a light bulb, electrons are converted into light and heat. The more electrons that are flowing, the more work the component can do: a bulb shines brighter as more current is applied.  We say that current can describe the quantity of electrons that are flowing along the circuit.

Current is measured in a unit called Amps (short for Amperes), and is written as a Capital A in values, but as a capital I in equations.

What is Voltage?

In order to get the current to flow through the circuit (moving the electrons from one end of the circuit to the other), we give the electrons a push. The force at which they are pushed, is the voltage.

A battery contains one or more storage cells of electrons (which will provide the current), but the important thing is that the battery has a potential difference between the Positive + and Negative terminals, and it is this potential difference between the + and – ends that acts like a pump to give the push. The more potential difference on our battery, the greater the push or voltage will be.

Let’s say we’re using a 1.5 Volt battery, which has 0 Volts at the negative end, but 1.5 Volts at the positive end. That potential difference pushes the electrons through the circuit, from the positive end of the battery to the negative end, giving a current (known as Conventional Current). If we connected a bulb (rated for 1.5V) in the circuit, those electrons flowing around will make the bulb shine brightly.

Figure 1 Electrons flowing around a circuit
Figure 1 Electrons flowing around a circuit

Voltage is measured in a unit called Volts, and is written as a capital V for both values and equations.

Current and Voltage have a direct relation to each other. If you adjust one, you affect the other, this is covered later on in Ohms Law.

What is Power?

By knowing the voltage that is applied to the circuit, and the current flowing through it, we can work out how much power the circuit is using, or to put it another way: how much of the current is being used up or consumed in the circuit. Again, Ohms Law provides the calculations that we will cover in a later topic.

Power is measured in a unit called Watts, and is written as a capital W in values, but as a capital P in equations.

Open and Closed Circuits

The circuit needs both ends of the battery connected to the circuit for the potential difference of the battery to push the current along. This is a Closed Circuit.

If one end is not connected, the circuit will not work, here, we say that the circuit is Open Circuit. If something has become disconnected, we often refer to this as a break in the circuit.

A switch can be added to the circuit:

  • When we make the circuit by turning the switch ON, the circuit is closed, and our bulb will light up.
  • When we break the circuit by turning the switch OFF, the circuit is open, so the light goes out.
Figure 2 Diagram showing switch OFF in circuitFigure 2 Diagram showing
switch OFF in circuit

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