Static electricity is a build-up of electric charge on the surface of an object, usually an insulator, made when electrons move from one material to another. You meet it when a rubbed balloon sticks to a wall, when your hair lifts towards a comb, or when you get a small zap from a door handle. The same physics, on a giant scale, produces lightning.
What is static electricity?
The word "static" means "staying still". In static electricity the extra charge stays put on an object instead of flowing round a circuit. That is only possible on an insulator such as plastic, rubber, glass or dry hair, because charge cannot flow through an insulator. On a conductor such as a metal rod, the charge spreads out and drains away to whatever the metal touches.
Every ordinary object is electrically neutral. It contains equal numbers of positively charged protons and negatively charged electrons, so the charges cancel out. Static electricity appears when that balance is upset. One object ends up with a surplus of electrons and the other with a shortage.
It helps to compare static electricity with the electricity in a circuit. In a circuit, charge flows steadily, and the size of the flow is the current. Here charge builds up and then, often, vanishes in a sudden spark. A full side-by-side comparison appears later in this article.
Examples of static electricity in everyday life
Once you know what to look for, examples of static electricity are everywhere.
- A comb and paper. Run a plastic comb through dry hair and it can pick up tiny scraps of paper.
- A balloon on your hair. Rub a balloon on your head and your hair lifts towards it. The same balloon will then stick to a wall.
- A shock from a door handle. Walk across a carpet in rubber-soled shoes, touch a metal handle, and a spark jumps to your finger.
- Clothes clinging together. Clothes tumbled in a dryer rub against each other and often stick when they come out.
- Dust on a screen. Dust is attracted to a television or monitor screen, which can pick up a slight charge.
- Lightning. The biggest natural spark of all, between clouds, the air or the ground.
Notice what these have in common. In each case two different materials were rubbed or pulled apart, charge was left behind, and the charge either attracted something or escaped as a spark. The sections below explain each step.
What causes static electricity? Charging by friction
To see where the charge comes from, remember the structure of the atom. Protons sit in the nucleus and are fixed in place, while electrons orbit outside. If you want a refresher, the lesson on atoms, protons, neutrons and electrons covers it. Because the protons are locked in the nucleus, only electrons can move from one object to another.
When two different materials touch and are then pulled apart, electrons can be left on the wrong side. Scientists call this triboelectric charging, from the Greek "tribo", meaning "to rub". Rubbing matters because it brings more of the two surfaces into contact. That is why a lot of everyday friction produces a lot of static.
The rule for GCSE is short:
- The material that gains electrons becomes negatively charged.
- The material that loses electrons is left with an equal positive charge.
Charge is not created by rubbing. It is moved from one place to another, so the two objects end up with equal and opposite charges, and the total charge is the same as before.
positive object = lost electrons · negative object = gained electrons
Polythene and acetate rods
The classic school demonstration uses two plastic rods and a cloth. Rub a polythene rod with a cloth and electrons transfer from the cloth to the rod. Rub an acetate rod with a cloth and electrons transfer the other way, from the rod to the cloth.
| Rod | Electrons move | Rod becomes | Cloth becomes |
|---|---|---|---|
| Polythene | From cloth to rod | Negative | Positive |
| Acetate | From rod to cloth | Positive | Negative |
Both rods are rubbed in the same way, yet they end up with opposite charges. Which material gives up electrons depends on the materials involved, and a list of that order is coming up in the next section of this article.
Counting the electrons
One electron carries a very small charge. The elementary charge is 1.602 × 10⁻¹⁹ coulombs (C), and at GCSE you can use 1.6 × 10⁻¹⁹ C. Everyday static charges are measured in nanocoulombs (nC), where 1 nC is 10⁻⁹ C. So even a tiny charge means a huge number of electrons.
number of electrons = charge ÷ 1.6 × 10⁻¹⁹ C
Try the calculator below. Type in a charge in nanocoulombs, say whether the object gained or lost electrons, and it works out how many moved.
The triboelectric series: which materials gain or lose electrons?
Some materials give up electrons more easily than others. A triboelectric series ranks materials from "tends to become positive" to "tends to become negative" when they are rubbed together. "Tribo" comes from the Greek for "rub".
The table below is one measured series from AlphaLab. The numbers are the measured charge affinity in nanocoulombs per joule, with wool set at zero. A higher value means the material tends to lose electrons and become positive. A lower value means it tends to gain electrons and become negative.
| Material | Charge affinity (nC/J) | Tends to… |
|---|---|---|
| Human hair / oily skin | +45 | Lose electrons (become positive) |
| Nylon | +30 | Lose electrons |
| Glass (soda) | +25 | Lose electrons |
| Paper (uncoated copy paper) | +10 | Lose electrons |
| Cotton | +5 | Lose electrons |
| Wool | 0 | Reference point |
| Acrylic (Perspex) | −10 | Gain electrons (become negative) |
| Polystyrene | −70 | Gain electrons |
| Polythene / polypropylene | −90 | Gain electrons |
| PVC (rigid vinyl) | −100 | Gain electrons |
| Latex (natural rubber, as in balloons) | −105 | Gain electrons |
| PTFE (Teflon) | −190 | Gain electrons |
To use the series, pick two materials. The one nearer the top becomes positive and the one nearer the bottom becomes negative. Rub a latex balloon on hair, for example. Hair is at +45 and latex is at −105, so electrons move from the hair to the balloon. The balloon becomes negative and the hair is left positive.
Like charges repel, unlike charges attract
Charged objects push and pull on each other. Two positive charges repel, and so do two negative charges. A positive and a negative charge attract. These forces act without the objects touching, so they are non-contact forces, like the pull between magnets.
The size of the force depends on the distance. The closer two charged objects are, the stronger the force between them.
Electric fields
The region around a charged object where another charge feels a force is called its electric field. The field is strongest close to the object and gets weaker further away. A second charged object placed in the field feels a force, and that force grows as the distance shrinks.
For an isolated charged sphere, the field lines are drawn straight out from the surface like the spokes of a wheel. By convention, the arrows point away from a positive sphere and towards a negative one. The lines are closest together at the surface, where the field is strongest. The same idea explains sparks, which you will meet in the next section.
Why does a balloon stick to a wall?
This is one of the most searched questions about static electricity, and the answer has four steps.
- Rubbing the balloon on your hair moves electrons from the hair to the rubber.
- The balloon is now negatively charged. The wall is neutral overall.
- Near the negative balloon, the charges in the wall shift slightly. Electrons in the wall are pushed a little away, so the surface nearest the balloon becomes slightly positive.
- The nearer positive charges attract the balloon more strongly than the further negative charges repel it, so the balloon is pulled to the wall and stays there.
So a charged object can attract a neutral one. That surprises many people, and it appears on lists of common physics misconceptions. The wall never gains or loses any electrons. They only shift a little within it.
The balloon eventually falls. Charge slowly leaks away through the air, especially when the air is humid, and the attraction fades.
Why does your hair stand on end?
Rub a balloon on dry hair and strands lift up towards it. First, hair and balloon have opposite charges, so they attract. Second, the hairs themselves pick up the same charge as each other, so they repel and spread apart.
The effect is dramatic on a Van de Graaff generator. The American physicist Robert J. Van de Graaff invented it in 1929. A moving belt carries charge up to a hollow metal dome, and tabletop versions reach the order of 100 kV. A person touching the dome gets the same charge on every strand of hair, so each strand is pushed away from its neighbours.
A charged polythene rod picks up small pieces of paper. Explain why, even though the paper is uncharged. (3 marks)
The polythene rod is negatively charged. It repels electrons in the paper slightly, so the side of the paper nearest the rod becomes positive and the far side negative. The opposite charge is nearer the rod, so the attraction is stronger than the repulsion. The paper is pulled towards the rod.
Detecting charge: the gold-leaf electroscope
How can you tell whether an object is charged? A gold-leaf electroscope does the job. It has a metal cap on a rod, with a thin strip of gold leaf attached, all inside a glass case. Bring a charged object near the cap and the leaf and the stem take the same charge. Like charges repel, so the leaf rises away from the stem.
A bigger charge makes the leaf rise further, so you can compare how strongly objects are charged. The English physician William Gilbert, who published De Magnete in 1600, built an early detector: a pivoted needle called the versorium.
Sparks and static shocks
A static shock is a small spark, and a spark is what happens when static electricity finally escapes. As more charge builds up on an object, the potential difference between it and its surroundings rises. The electric field near the object becomes stronger. Eventually the field is strong enough to make the air conduct, and charge crosses the gap in an instant. You see a flash, hear a crack and feel a sting.
The door-handle zap follows these steps:
- You walk across a carpet in rubber-soled shoes. Rubbing builds up charge on your body, because rubber is an insulator and the charge cannot drain away.
- You reach for a metal door handle. As your finger gets close, the field between you and the handle becomes strong.
- The air in the gap breaks down and a spark jumps across.
- Charge flows through the metal and your body is back to neutral.
Static shocks are usually not harmful, but they can damage sensitive electronic parts. They can also ignite flammable gases. Another way charge leaks through air near high voltage is described in this post about corona discharges on high-voltage lines.
Why static shocks are worse in winter
If you seem to get more shocks in winter, dry air is the likely reason. Dry air lets far more charge build up on you. Moisture in humid air makes surfaces slightly conducting, so charge leaks away before it can build up. The ESD Association, which studies electrostatic discharge, measured typical voltages at low and high relative humidity.
| Activity | Dry air (10–25% humidity) | Humid air (65–90% humidity) |
|---|---|---|
| Walking across a carpet | 35,000 V | 1,500 V |
| Walking across vinyl tile | 12,000 V | 250 V |
| Worker at a bench | 6,000 V | 100 V |
| Plastic bag picked up from a bench | 20,000 V | 1,200 V |
The carpet figure drops from 35,000 V to 1,500 V, a fall of more than twenty times, just because the air is damper. Dry air is the key: damp air lets charge leak away before it can build up.
How to get rid of static electricity
You cannot switch static off, but you can make it much less annoying. Researchers who study it suggest these steps:
- Raise the humidity indoors, for example with a humidifier.
- Moisturise your skin.
- Choose your footwear carefully. Rubber soles on carpet are a classic cause of body charge, and they are worse than leather.
- Touch a metal object such as a key to a metal surface before reaching for the handle. The spark then jumps from the key and you feel much less.
Lightning: static electricity on a giant scale
According to the US National Severe Storms Laboratory, "lightning is a giant spark of electricity in the atmosphere between clouds, the air, or the ground". It is the same process as the door-handle zap, only much bigger.
Inside a thundercloud, soft hail called graupel collides with ice crystals. These collisions separate charge. In the main pattern, the graupel carries negative charge in the middle of the storm, while the ice crystals carry positive charge higher up. There is often a small positive region below the main negative region.
Air is a good insulator, so it holds the opposite charges apart for a while. Once enough charge has built up, the insulation breaks down and charge rushes across in a flash. Lightning can stay inside a cloud, which is called intra-cloud lightning, or it can strike the ground, which is cloud-to-ground lightning.
Close to the ground, within roughly 90 metres, trees, bushes and buildings send up sparks to meet the channel coming down. Tall objects are therefore more likely to be struck, though lightning can also hit open ground.
The channel heats the air to around 28,000 °C for a moment, which is much hotter than the surface of the Sun. The air expands explosively, and that is the thunder you hear.
Charge and voltage also explain why birds can sit on a power line. A bird on a single wire does not make a path to earth, so no current flows through it. You can read more in why birds perch on electrical wires.
How far away is the storm?
Light reaches you almost instantly, but sound takes time. Sound travels about one third of a kilometre per second. Count the seconds between the flash and the thunder, then divide by three to get the distance in kilometres. Divide by five for miles.
distance (km) ≈ time (s) ÷ 3
A short history of static electricity
The word "electric" has a static-electricity story behind it. In 1600 the English physician William Gilbert published De Magnete. He was Elizabeth I's physician from 1601 to 1603. Gilbert studied materials that attract light objects when rubbed. He called them "electricus", meaning "like amber", because the Greek word for amber is "elektron". That is where our word "electric" comes from.
In June 1752 in Philadelphia, Benjamin Franklin flew a kite in a storm to show that lightning is electrical. The kite was not struck by lightning. It picked up charge from the storm, and a spark jumped from a metal key to his knuckle. He also stored charge in a Leyden jar and went on to perfect the lightning rod.
Uses of static electricity
Static electricity is more than a nuisance. Engineers use the forces between charges to do useful work. Its uses depend on charged objects attracting or repelling each other.
Photocopiers and laser printers
A photocopier uses charge to place toner exactly where the text is. An image of the document is projected onto a positively charged plate or drum. Where light falls on the pale areas of the page, the charge is lost. The dark text areas keep their charge. Negatively charged toner powder then sticks to the charged areas, is transferred to paper and is heated so that it stays fixed. Laser printers work in a similar way, and inkjet printers can use charged droplets.
Electrostatic paint and crop spraying
Spray guns for car paint and for insecticide can give the droplets an electric charge. Every droplet gets the same charge, so the droplets repel one another and spread into a fine, even spray. They are also attracted to the oppositely charged or earthed target, so less of the spray drifts away and the coating wraps round to cover hidden sides.
Electrostatic precipitators
Burning fuel produces smoke and dust. An electrostatic precipitator cleans the gases in a chimney before they leave. Negatively charged wires give the smoke particles a charge, and the particles are then attracted to oppositely charged collecting plates. Particles that stick to the plates are removed, so less of this pollution escapes. For the wider picture, see this article on air pollution.
The Van de Graaff generator in the carousel above is a showpiece rather than a tool. It builds up static charge on a dome. A power-station generator is different, because it uses electromagnetic induction to push a steady current. If you are curious, how generators work explains the contrast.
Dangers of static electricity
Most static sparks are harmless. The danger comes when a spark meets something that burns easily.
- Fuel. Fuel is a liquid insulator. As it flows through a pipe, friction charges it. A spark in the presence of fuel vapour could cause a fire or explosion. Non-conducting fuel pipes can reach potentials as large as 90 kV.
- Aircraft refuelling. The aircraft is connected to earth by a copper bonding line during refuelling, so charge can drain away safely.
- Road tankers. According to the UK Health and Safety Executive, when offloading flammable liquids the driver must first connect the tanker to the earthing connection at the offloading point.
- Dust explosions. Static discharge is a known danger in grain elevators, where dust can explode.
- Electronics. A static discharge can damage sensitive electronic parts, which is why people who handle them take precautions.
Earthing: making static electricity safe
Earthing means connecting a charged object to the ground with a conductor, usually a copper wire. Charge can then flow away and the object becomes neutral. Pumps and pipes that carry fuel are earthed so that any excess charge has a safe route away.
The direction of the electron flow depends on the charge on the object. Think about what the object needs in order to become neutral again.
Static electricity vs current electricity
Students often mix these two ideas up. Both involve electric charge, but they behave very differently.
| Feature | Static electricity | Current electricity |
|---|---|---|
| Charge | Stays on an insulator | Flows through a conductor |
| How it starts | Friction or contact between materials | A potential difference from a cell or supply |
| Release | A sudden spark or shock | A continuous flow while the circuit is complete |
| Examples | Rubbed balloon, door-handle shock, lightning | A bulb lit by a battery |
In a circuit, the amount of charge that flows depends on the current and the time:
Q = I × t
Here Q is charge in coulombs, I is current in amperes and t is time in seconds. To trace the flow in a real circuit, try the direction of current practical.
Test yourself on static electricity
Frequently asked questions about static electricity
What is static electricity in simple terms?
Static electricity is electric charge that builds up on the surface of an object and stays there instead of flowing. It usually forms on insulators when two materials are rubbed together and electrons move from one to the other. The object is then positively or negatively charged until the charge escapes.
What causes static electricity?
Static electricity is caused by electrons moving from one material to another when the two touch and separate, as in rubbing. The material that gains electrons becomes negative and the one that loses them becomes positive. Insulators hold the charge in place, so it cannot flow away.
What are some examples of static electricity?
Common examples include a rubbed balloon sticking to a wall, hair rising towards a comb, clothes clinging together after a tumble dryer, a shock from a door handle after walking on carpet, dust gathering on a screen and lightning. Photocopiers and electrostatic paint sprayers use it on purpose.
Do protons move in static electricity?
No. Protons are fixed in the nucleus of an atom, so they cannot be rubbed off. Only electrons move between objects. An object that is positively charged has lost electrons, which leaves it with more protons than electrons. An object that is negatively charged has gained electrons.
Why do I keep getting static shocks?
Shocks are most common in dry air, because humidity helps charge leak away. Rubber-soled shoes on carpet build up charge on your body, and a metal handle gives it a path to escape as a spark. Raising the humidity and touching a key to the metal first can help.
Is static electricity dangerous?
Everyday static shocks are usually not harmful, but static can damage sensitive electronics and ignite flammable gases or fuel vapour. That is why aircraft and road tankers are earthed when fuel is moved. Lightning, which is static electricity on a giant scale, is very dangerous. Go indoors when you hear thunder.
How do you get rid of static electricity?
To get rid of static charge, give it a path to earth. Touch a metal object, and raise the humidity indoors with a humidifier. Moisturising your skin and choosing leather-soled rather than rubber-soled shoes also helps. Industry connects equipment to earth with a conductor so excess charge drains away.
What is the difference between static and current electricity?
In static electricity, charge builds up and stays on an insulator until it escapes as a spark. In current electricity, charge flows continuously through a conductor in a complete circuit because of a potential difference. Charge flowing is the current, and the amount that flows is the current multiplied by the time.
Is lightning static electricity?
Yes. Lightning is a giant spark. Collisions between graupel and ice crystals in a storm cloud separate charge, and when enough builds up the air breaks down and charge rushes across. It follows the same physics as a small static shock, but on a much larger scale.
