In its simplest terms, electricity is the movement of charge, which is considered by convention to be, from positive to negative. No matter how the charge is created, chemically (like in batteries) or physically (friction from socks and carpet), the movement of the discharge is electricity.

This flow of electrical charge is referred to as electric current. There are two types of current, direct current (DC) and alternating current (AC). DC is current that flows in one direction with a constant voltage polarity while AC is current that changes direction periodically along with its voltage polarity. Thomas Edison and Alessandro Volta were pioneers in DC current and wrote much of electricity’s history. But as societies grew the use of DC over long transmission distances became too inefficient. Nikola Tesla changed all that with the invention of alternating current electrical systems. With AC it is possible to produce the high voltages needed for long transmissions. Therefore today, most portable devices use DC power while power plants produce AC.

The amount of current is based on the supply voltage and the resistance in the circuit. Current is measure in units of Amperes, or Amps for short. The current will prefer to take the path with the lowest resistance. 

When something has an electric charge, it means that there is an imbalance of electrons, either too many or too few. When we measure the difference in electric charge between two points, it is known as voltage. Typically, the earth is used as a common reference point, so when a circuit has 120 Volts, that is the difference between the source voltage and the ground’s voltage. 

An example of this is often seen when someone is working without wearing properly insulated footwear. If the worker comes in contact with something that is electrically charged, like an exposed wire or the terminal on a battery, they will experience an electrical shock because the body offers a path to ground with less resistance than the surrounding air. This means the body has become part of the circuit. 

How much opposition the conductor or metal wire presents to the electric current flow is the electrical resistance. The lower the resistance, the easier current will flow. Think of current like water flowing through a pipe, if the pipe is small there is more resistance to water flow, if the pipe is large the water will flow much easier. A larger wire size has less resistance and will allow more current to flow. 

Electrical resistance is measured in units of Ohms. Resistance is also affected by the material itself. Most metals are good conductors, which means they have low resistance, because their electrons can be gained and lost very easily. Insulators, like plastic or wood, have electrons which are much more tightly bound to the nucleus, which means that they are harder to move around. Also, as a material heats up, its resistance increases, and the resistance decreases as it cools down. 

Key terms include:

• energised circuit - Electrically connected to or having a source of voltage.

• de-energised circuit - Free from any electrical connection to a source (disconnected).

• voltage (E) is the difference in charge between two points.

• current (I) is the rate at which charge is flowing.

• resistance (R) is a material’s tendency to resist the flow of charge (current).

ACTIVITY

Read through the wesite (left) to revise basic electrical theory, particularly revising Ohm's Law which we have learnt previously with voltage as 'v'.

Insulation is a non-conductive material in a cord’s construction. It is also sometimes referred to as dielectrics in radio frequency cords. Insulation is resistive to current leakage, which prevents the conductor’s current from touching other conductors and cords nearby. It also maintains the wire’s material integrity by shielding it from environmental threats like heat and water. The effectiveness and longevity of a wire depend on the insulation.