What Is Electricity?

Electricity is energy carried by the flow of electric charge, usually electrons moving through metal wires. It is one of the most useful forms of energy ever discovered. Almost every modern convenience runs on electricity: lights, fridges, computers, phones, trains, traffic signals. We have only been using electricity for around 150 years, but it has transformed the world more in that time than perhaps any other technology in history.

  • What it isFlow of electric chargeUsually electrons in wires
  • CurrentRate of charge flowAmperes (A)
  • VoltagePush behind the currentVolts (V)
  • ResistanceOpposition to flowOhms
  • UK mains230 V, 50 HzStandard household
  • Electron speedVery slow driftBut signal flows near light speed

What is electric charge?

Charge is a basic property of certain subatomic particles. There are two kinds:

  • Positive charge: carried by protons in the nucleus of every atom.
  • Negative charge: carried by electrons that orbit the nucleus.

Opposite charges attract; like charges repel. Most things around you are neutral: they have equal numbers of protons and electrons, so the positive and negative cancel out and you do not feel the charges. When charges are unbalanced (more electrons than protons, or vice versa), the object becomes charged.

Static and current electricity

Two main kinds of electricity:

  • Static electricity: charge that has built up on an object and is not moving. Examples: getting a shock from a doorknob, hair standing up after rubbing a balloon.
  • Current electricity: charge that flows through a material (usually a wire). Powers nearly all our devices.

(See static vs current electricity for more.)

How electricity flows

In a metal wire, the outer electrons of each atom are loosely held and can move freely. When you connect a battery (or any electrical power source) to the wire, the battery acts like a pump: it pushes electrons through the wire from one terminal to the other. The flow of electrons through the wire is the electric current.

Strangely, by convention, the "direction of current" is defined as the direction positive charges would flow, which is OPPOSITE to the direction electrons actually flow. This is a historical leftover from before scientists knew electrons existed. The maths works out either way.

Fact Electrons themselves move very slowly through a wire (just a few millimetres per second). But the electrical signal travels almost at the speed of light. The reason: when you push electrons in at one end, all the other electrons in the wire shift along immediately, like a tube already full of marbles. The push at one end pops a marble out the far end nearly instantly.

The three key measurements

  • Voltage (V): how hard the battery pushes the charge. Measured in volts. A UK mains socket gives 230 V; a torch battery gives 1.5 V.
  • Current (I): how many charges flow per second. Measured in amperes (amps, A). A kettle draws around 10 A; a phone charger maybe 1 A.
  • Resistance (R): how strongly the wire resists the flow. Measured in ohms. A thin filament has high resistance; a thick copper wire has low resistance.

These three are related by Ohms law: V = I x R. Higher voltage pushes more current. More resistance allows less current for the same voltage. Engineers use this equation in almost every electrical calculation.

How we generate electricity

Most electricity in the UK and the world is made by spinning a wire coil between magnets (or a magnet between coils). Movement of magnets near coils creates voltage, which drives current. This is called electromagnetic induction, discovered by Michael Faraday in 1831. The spinning is usually done by:

  • Steam turbines: water boiled by burning gas, coal, biomass or nuclear fuel turns into high-pressure steam, which spins a turbine.
  • Wind turbines: wind spins blades directly.
  • Hydroelectric: flowing water (from a dam) turns a turbine.
  • Tidal and wave: the rising and falling sea turns underwater turbines.
  • Solar panels: an exception. They produce electricity directly from sunlight using photovoltaic cells, no spinning involved.
Did you know? The electricity that comes out of your wall socket changes direction 50 times every second in the UK (60 times per second in the USA). This is called alternating current (AC). Batteries, on the other hand, push current in only one direction (DC, direct current). Modern devices like phones convert AC from the wall into DC for their circuits using small adapters (the "wall warts" plugs).

Why electricity is dangerous

Electricity flowing through the human body can be deadly. Even quite small currents (just 0.1 A) flowing through the heart can stop it beating. Voltages over 50 V are considered hazardous. UK mains at 230 V can kill in seconds.

That is why:

  • Plugs are designed so you cannot easily touch live metal.
  • Cables have insulation around the wires.
  • Bathrooms use special low-voltage shaver sockets only.
  • Outdoor sockets must be RCD-protected (a safety device that cuts power within milliseconds if it detects a short circuit or leak).
  • You should never play with mains-powered equipment, and never insert anything into a wall socket.
Try this Rub a plastic comb on a wool jumper or your hair to give it static electricity. Hold the comb close to (but not touching) a fine stream of water from a tap. The water bends towards the comb, attracted by the electrical force between the negative comb and the slightly positive water molecules. You are watching electricity at work, without any current flowing at all.
Deeper dive: the war of the currents

In the 1880s, two great American inventors went head to head in one of the bitterest commercial rivalries in history: the War of the Currents.

Thomas Edison, the famous inventor of the light bulb and the phonograph, championed direct current (DC). His New York power station, opened in 1882, supplied DC at low voltage (around 100 V) to nearby buildings.

The problem was distance. DC at low voltage loses huge amounts of energy in the wires over long distances. Edisons system could only serve customers within a kilometre or so of each power station.

Nikola Tesla, a brilliant Serbian-American immigrant working for Edisons rival George Westinghouse, promoted alternating current (AC). AC could be easily converted between low and high voltages using a device called a transformer (which only works with AC). Sending electricity long distances at very high voltage (tens of thousands of volts) loses far less energy. The voltage is then transformed back down to safe levels just before reaching homes.

Edison fought back fiercely. He campaigned that AC was too dangerous, holding gruesome public demonstrations electrocuting animals with AC to scare the public. He even encouraged the use of AC for the new electric chair in the USA, hoping people would associate AC with death.

It did not work. AC was simply too efficient for long-distance transmission. By the 1890s, AC had clearly won. The 1893 World Fair in Chicago was lit by Westinghouses AC system, and the 1895 hydroelectric power station at Niagara Falls used AC. Today, almost the entire worlds electricity grid uses AC.

Edison eventually accepted defeat (and quietly bought stock in Westinghouses companies). The War of the Currents shaped the world we live in: every plug socket, every power line and every transformer hanging on a pole owes its design to Teslas and Westinghouses victory.

For more, see circuits and conductors and insulators.