Elements, Atoms, Electrons

Since ancient times it has been theorised that everything is made of a number of fundamental substances called Elements, and that elements are made up of tiny pieces called Atoms.

During the 17th Century Enlightenment, the early Chemists determined that the substances that make up our world are either Pure Elements (made up of one kind of Atom) or Compounds (made up of several different elements in fixed combinations).

An Atom can be thought of as a tiny compact Nucleus surrounded by moving particles called Electrons. The electron has a property that we call “Electromagnetic Charge” which comes in two kinds. We denote the charge on the Electron as “Negative charge”, and that on the particles in the nucleus (Protons) as “Positive charge”. If you imagine the Sun at the centre of our solar system as the Nucleus, and the far flung Planets as Electrons, this is a helpful analogy. Like the Solar system, an Atom is largely empty space. Where the force of gravity that holds the solar system together only pulls, the electromagnetic force can both push and pull. Two like charges (both negative or both positive) will repel each other, whereas a negative and positive charge will attract (this is the origin of our cliche “opposites attract”).

Chemists divide elements into two basic kinds, Metals whose Electrons can be persuaded to jump from one atom to a neighbour, and Nonmetals whose electrons largely stay put. There are about 90 kinds of naturally occuring elements. Commonly encountered metallic elements are Copper, Iron, Aluminium, Gold, and Silver. Commonly encountered non-metals are Oxygen, Carbon, Sulphur and Chlorine.

In metals, it is the movement of electrons from one atom to another that we experience as Electricty, be it in the form of Lightning, Static Electricity, or Electric Current (where large numbers of electrons flow through a metal something like water through a pipe). We also call metals “Conductors”, and nonmetals “Insulators” or “Non-conductors”. (There’s also a small group of elements, including Silicon, that are “Semi-Conductors, which we will come back to later).

Moving charges create a “Magnetic Field” which, like the force of gravity, can affect objects at a distance. We manipulate electrons to use their magnetic field to work, such as turning an electric motor.

Voltage and Current

You can think of the flow of electrons a bit like water.

The “water pressure” is called Voltage, which we measure in Volts. Voltage is a measure of how much each electron “wants” to move (even if they cant), for this reason voltage is also referred to as a “potential difference”, that is an electric charge that will move if it is provided with a conductive path. For example the electricity in a AA battery is at 1.5 Volts, and that in our houses is at 240 Volts. You probably already understand that the electricity in our home wiring is more “powerful” than the electricity from a AA battery.

Like an atom, a source of electric power has a positive and and a negative side. We consider that power flows from the positive to the negative (even though, in a historical accident, the electrons actually move in the opposite direction). Imagine a garden hose filled with marbles; you could not add another marble unless you let one out. So it is with electrons, even if we apply a voltage (pressure) to electrons using one side of a power source, they will not move unless they can return to the other side (like marbles exiting a tube. In order to use electricity to do work, we need to provide an Electric Circuit that lets the electrons move from one terminal of the power source, to the other. These are the two ends of a battery, or outside two pins on a USB cable, or two of the prongs of a household power cord.

When electrons are actually moving, we measure how many electrons are passing a given point per second as Electric Current, measured in Amperes (often called “Amps”). Your phone charger typically delivers Five Volts, at One half of an Ampere (or 500 Milli-Amperes), so we would rate it as “5v, 500mA”.

The amount of “Power” (measured in Watts) available from an electric current, is the product of the voltage and current. So a power supply that can deliver 5v, 500mA can also be said to 5 x 0.5 == 2.5 Watts.

A flashlight uses around one Watt, laptop computer around 50 Watts, and a kitchen kettle approximately 5000 Watts.


Not all substances conduct electric current with the same ease. Like a pipe that is blocked, some substances resist the flow of electricity. When a current is being resisted, the substance resisting it heats up. Another way of saying this is that the electrical energy is converted to heat. We use this effect to do work also (for coooking, heating, and lighting), but it can also be a problem (for example when your computer or phone gets hot when it is working hard, this is waste heat from resistance in its wiring).

We use Copper, Aluminium and even Gold in our electrical wiring because these metals have good conductivity (which is the same as saying low reistance). We sometimes deliberately use low-conductivity metals in devices such as heaters, kettles and incandescent lightbulbs.

We measure Resistance in Ohms.

When electrons enter a conductor, they carry some amount of energy each (in fact, a Volt is defined as one Joule per Coulomb (the unit of charge)). The resistance of the conductor will consume some of this energy (converting it heat), and so the electrons leaving it will have less energy, resulting in a “voltage drop”. Voltage can also be affected by magnetic fields, an electric motor will rob energy from the electrons and use it to do work, wherease an electric generator will convert movement of a magnetic field into energy added to electrons, resulting in increased voltage.

One of the fundamental rules of electronics is Ohm’s Law which lets us predict how an electric voltage (or potential difference) will flow through a conductor.

Ohms law states that V=IR (alternatively I=V/R or R=V/I) (where V is voltage volts, I is current in Amperes, and R is resistance in Ohms). This allows us to say that if a current of one Ampere flows through a conductor of resustance one Ohm, then a voltage drop of one Volt will occur.

The inverse relationship applies–if we apply 5 volts to a resistance of 10 ohms, then we can predict that a current of 510 = 0.5 Amperes (or 500mA) will flow.

You don’t need to understand or memorise this in detail right now (but you will come to in time). For now it is enough to recognise that we use power supplies like batteries to apply voltage, and our electric circuits contain components that “use up” that voltage to do useful things. If we need to, there are rules that let us measure or predict how the electricity will behave.