Discover what electricity really is and how centuries of science have managed to tame its awesome powers!
From lightning bolts to electric circuits, electricity has many faces, but all are linked to the existence and movement of electrical charge. When it comes to powering the gadgets in our homes, the star of the show is the electron – a minuscule but significant particle found in every atom.
An atom consists of negatively charged electrons that orbit a nucleus made up of positively charged protons and electrically neutral neutrons. Opposite charges attract and so electrons are held captive by the nucleus’s positive charge. Normally, there are equal numbers of electrons and protons, cancelling out each other’s charges and leaving the atom with a neutral charge overall. until electricity comes along to shake things up, that is.
Inside a metal, atoms rub elbows in a tight lattice, sharing one or two of their outermost electrons which meander in all directions. Under the right conditions, these free electrons can be persuaded to travel en masse in one direction. The resulting movement of charge is what we call an electric current.
Electric currents can also be carried by ions – charged particles which occur, for example, when an atom loses or gains an electron. For instance, when salt (sodium chloride) dissolves in water, positively charged sodium ions and negatively charged chlorine ions are freed from the shackles of solid salt and roam freely.
Materials that contain high densities of wandering electrons or ions are called conductors. Metallic conductors like copper are ubiquitous in electrical appliances, but ionic conductors get their share of the limelight inside batteries and even living creatures. Other materials, such as rubber or glass, are configured in such a way that their electrons cling tightly to atoms, making it difficult for a flow of electrons to occur; these are insulators.
All electric currents are not created equal, with several different factors affecting the flow of electrons. When a battery is connected to a light bulb, the current that flows depends on the voltage or potential difference applied by the battery and the resistance of the light bulb.
Imagine a pump forcing water through a pipe: the battery is the pump and the voltage is the ‘pressure difference’ across the pipe. Increase the voltage and the current increases too. The bulb’s resistance, expressed in ohms, is a measure of how difficult it is for the current to pass. Akin to forcing water through a partly blocked pipe, the greater the resistance, the smaller the end current: ie current (amps) is the voltage (volts) divided by the resistance (ohms).
Electricity in nature
A fork of lightning tearing across the sky is one of the most vivid depictions of an electrical current, but lightning also exemplifies one of electricity’s other faces: static. While electric current is all about moving charges, static electricity is the buildup of charge in one place. In the case of lightning, opposite charges accumulate at the base of a storm cloud and on the ground, generating an increasingly powerful potential difference which is eventually discharged in a blaze of light.
We often witness slightly less spectacular forms of static in the form of little electric shocks. When different materials come into contact, they frequently steal electrons from each other, with some holding on to this charge better than others. The simple act of walking across carpet or taking off a jumper can thus cause your body to accumulate a negative charge. When you touch a conductive object like a door handle, the excess electrons can escape through your fingertips, startling you with an electric shock in the process. Moisture in the air helps to dispel static charges, making these shocks far more common in dry weather.
Static may be a minor inconvenience, but your body – like those of all living creatures -can’t function without electricity. Right now, tiny electric impulses are racing through you, relaying messages to and from your brain through a dense network of neurons. These cells create an electric potential by controlling the flow of charged ions across their membranes. When stimulated, they reverse this potential, passing on a signal.
Through these electrical impulses, your nerves alert your brain to pain but also convey the multitude of sensations captured by sight, sound, taste, touch and smell. Analysing this input, your brain then uses the same means of communication to tell your muscles to contract, controlling conscious movement but also the subconscious working of organs such as the heart. Unlike the slow-paced chemical communication of, say, hormones, electric impulses allow these important messages to be transmitted almost instantaneously.
The voltages generated by your body are no greater than 0.1 volts, but some animals have evolved far more sophisticated systems to produce electricity. Electric eels, for instance, deliver powerful jolts to stun prey or deter predators. One of numerous electric fish species, they achieve this thanks to as many as 6,000 electrocytes – disc-shaped cells which generate an electric potential. Each of these cells creates a tiny internal negative charge by pumping out positively charged ions.
Under the brain’s instructions, an electrocyte opens channels which allow positive ions back in, but only on one side of the cell, creating a temporary electric potential across the cell. By stacking up all these tiny batteries and firing them in unison, the electric eel can create an imposing 650-volt shock – more than enough to put a would-be assailant off its lunch.
Other aquatic animals such as sharks have taken a different approach, tuning in to the faint electrical signals emitted by their prey in the water. Since all animals’ brains and bodies use electricity, it’s an effective way to track down just about any creature in murky waters.
Nature may boast some impressive electrical feats, but humans have dreamt up their own methods to generate electricity on demand. The mains power which is lurking behind the sockets in your home is provided by power plants, which typically transform chemical or mechanical energy into electric energy.
Most large-scale electricity generation relies on a nifty principle called induction. Renowned British electricity pioneer Michael Faraday was the first to discover that a varying magnetic field could ‘induce’ a potential difference in a conductor. In other words, producing the voltage needed to create an electric current is simply a question of exposing a conductor to a fluctuating magnetic field.
Inside most power plants, the first step in the process is heating water, which is usually achieved by burning fossil fuels such as coal to release their chemical energy. Just like in a kettle, as the water heats up it gives off high-pressure steam, which is directed towards a turbine. Using this turbine to spin a magnet inside a conducting coil of wire (or vice versa) creates the varying magnetic field needed to induce a current in the wire.
Fossil fuels still account for the vast majority of energy produced worldwide, but concerns about global warming and the limited supply of resources like coal make renewable energy sources an increasingly attractive option.
Some renewable energy technologies use the same blueprint as fossil fuel plants, simply finding different ways to heat water. Nuclear power plants harness the heat unleashed by nuclear fission reactions, while geothermal plants exploit the intense heat at Earth’s core.
Other forms of renewable energy follow the same basic principles but take a few shortcuts. Instead of producing heat and steam, they set turbines into motion by capturing mechanical energy directly from flowing water, wind, waves or ocean tides. Although the initial energy source is different, induction is still the underlying principle at work.
Solar power, on the other hand, employs a radically different approach. Solar (or photovoltaic) cells convert sunlight into electricity by taking advantage of the photoelectric effect: the ability of matter to emit electrons when light is shone upon it. Inside a solar cell, photons – the minuscule packets of light energy in sunlight – knock electrons off silicon atoms. These are then organised into an electrical current thanks to silicon’s semi-conductive properties, which allow an electrical imbalance to be created and maintained across the solar cells.
Solar power is far more portable than your average power station or wind turbine, making it the ideal power source for everything from pocket calculators to deep-space satellites. The number one choice for portable power, however, is of course the battery.
A battery stores chemical energy which it then converts into electricity when its terminals are connected to a circuit. Chemicals inside the battery react together, releasing electrons from the battery’s negative terminal. These electrons then flow through the circuit before being collected by another chemical reaction at the positive terminal. The chemicals fuelling these reactions are gradually depleted, though rechargeable batteries allow the reactions to be reversed, replenishing the battery’s charge.
However, one of the most exciting modern technologies for portable power has to be hydrogen fuel cells. Similar to batteries, these use chemical reactions to generate electricity, combining hydrogen and oxygen, with heat and water as the only by-products. Hydrogen fuel cells already power a number of buses and forklift trucks, and the first commercially available hydrogen-powered cars are expected to hit the market in the next few years. Hydrogen’s capacity to store energy leads a number of experts to speculate that it will power entire societies in the future.
In the meantime, the vast majority of our daily energy needs are still met by power stations. Generating the electricity is, however, just the beginning of the story – next comes its complex journey to our homes.
How electricity gets to your home
Electricity distribution is taken care of by a ‘grid’, a national network of transmission lines connecting power stations to local substations and finally to the homes of consumers. In the US alone, there are over 300,000 kilometres (186,000 miles) of wiring dedicated to electricity distribution. The UK has just one network – the National Grid – while there are three different networks in operation in the States.
The grid cannot store electricity, so the output from power stations must mirror people’s varying needs, from the moment you put the kettle on in the morning until you switch off your bedside lamp at night. As a result, at peak periods electricity is often imported from power stations far away, making efficient transmission a must.
Before heading to your home, the electricity generated by a power station has its voltage boosted. When a wire transmits a large electric current, resistance causes it to lose energy as heat. The bigger the current, the more resistance is created and so the greater the waste. The solution is to ramp up the voltage, meaning the same amount of energy can be transported by a much weaker current.
Inside substations, there are clusters of transformers which progressively step up the voltage created by the power station’s generator. Once again, induction plays a vital role. A simple transformer consists of a dual electromagnet: a doughnut or horseshoe-shaped iron core with two distinct coils of wire wound around it. The first coil is connected to the generator, creating an electromagnet. The current produced by a power station is alternating (AC), meaning the flow of electrons periodically changes direction (as opposed to a battery which provides a constant flow of electrons in one particular direction – ie direct current, or DC). The electromagnet therefore produces a varying magnetic field, enabling it to induce a voltage in the second coil.
The size of this second voltage is determined by how the wire coils are set up. If the incoming wire has ten loops and the outgoing wire just five, the voltage will be doubled. The opposite arrangement is used to reduce voltages.
With its voltage increased dramatically, electricity is ready to hit the road on the electrical equivalent of a high-speed motorway: high-voltage transmission lines.
High-voltage lines stretch over huge distances, held well out of reach by towering electricity pylons. Before entering towns and cities, substations bring the voltage back down to safer levels. Cables then usually transport electricity underground for extra safety.
Further transformers supply end users with different voltages, with relatively high voltages provided for industrial purposes and lower voltages reserved for domestic use.
Anyone who’s ever taken a hair dryer across the Atlantic will know that countries use different voltages as well as different plug shapes. Largely for historical reasons, most countries worldwide (including the UK and Australia) use 220, 230 or 240 volts, whereas North and Central American countries have almost all opted for 120 volts.