# Electricity and Circuits

## WHAT IS ELECTRICITY?

Electricity is a form of energy resulting from charged particles (atoms and their electrons) either statically as an accumulation of charge or dynamically as a current.

An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire.

Static electricity is typically produced by friction. It stays put and does not “flow” like current electricity.

Atoms and electrons:

Atoms are tiny particles of matter. They are the building blocks of the Universe. The center, or nucleus, of an atom contains protons, which are positively charged particles and neutrons, which have a neutral charge. The negatively charged particles that revolve around the atoms are called electrons.

An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire.

Early researchers thought electricity flowed from positive to negative. They discovered later on that it actually flows from negative to positive.

The old theory is called "conventional current flow." What we know now is "actual current flow".

Electrical power is measured in watts. In an electrical system, power is equal to the voltage multiplied by the current.

## OHM'S LAW

This law is one of the fundamental relationships found in electronic circuits – for a given resistance, the current is directly proportional to the voltage. In other words, if you increase the voltage through a circuit whose resistance is constant, the current goes up. If you decrease the voltage, or if the resistance goes up but the voltage is constant, the current goes down.

This relationship can be expressed as a simple mathematical formula:

V = I x R

R is for resistance. V is for voltage. I is for current.

## CIRCUITS

A circuit is a closed loop that electrons can travel in. A single series circuit contains four parts: a power source, a load, the current and a switch. The power source provides energy for the electricity to travel along the circuits. The load is the device that the circuit is designed to power. Wires allow the current to travel along the circuit. The switch is a device that can open or close the circuit without having to disconnect anything. The picture on the right shows how a single series circuit works. The battery is the power source. The light bulbs are the load. The wires are the connectors, and there is a switch that can be flipped to close the circuit without having to disconnect the wires.

A parallel circuit gets its name from having multiple (parallel) paths to move along. Charges can move through any of several paths. If one of the items in the circuit is broken then no charge will move through that path, but other paths will continue to have charges flow through them. Parallel circuits are found in most household electrical wiring. The picture below is an example of a parallel circuit.

Conductors and insulators:

Conductors are things that carry electricity along. Copper and silver are excellent conductors. Insulators keep electricity from passing through. Styrofoam and rubber are insulators.

Resistors:

A resistor is used to limit the current flowing in a circuit. Too much current flowing through a component can damage it.