Uses and Dangers of Static Electricity

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 2.26 — Explaining electrostatic phenomena in terms of electron movement (bold P statement — Paper 2 only)
• 2.27 — The dangers of electrostatic charge, such as when fuelling aircraft and tankers (bold P statement — Paper 2 only)
• 2.28 — Uses of electrostatic charge, such as photocopiers and inkjet printers (bold P statement — Paper 2 only)

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Charge that has been separated does not stay separated for ever. If enough of it builds up in one place, the attraction across the gap becomes strong enough to tear electrons off the atoms in the air itself, and the air briefly becomes a conductor. Electrons rush across, and there is a SPARK — a sudden discharge, with heat, light and a crack of sound. Everything on this page, useful and dangerous alike, is that one event being either exploited or prevented.

The danger, in the order the examiner wants it

1. Two surfaces move against each other — fuel flowing through a hose, a lorry's tyres on a road, a belt running over a pulley, an aircraft moving through the air.
2. FRICTION transfers electrons from one to the other, so charge builds up on the insulating surfaces and cannot flow away.
3. The charge continues to accumulate, because an insulator gives it nowhere to go.
4. Eventually the charge is large enough to cause a SPARK across a gap to something at a different potential.
5. If the surroundings contain fuel vapour, dust or powder, that spark can IGNITE them, causing a fire or an explosion.
6. THE REMEDY IS EARTHING: connect the object to the ground with a conductor, so the charge flows away continuously and never builds up enough to spark.

The specification names fuelling as the example, and it is worth knowing why it is the worst possible case. Fuel is an insulator, it flows fast through the hose, and it is surrounded by exactly the vapour that a spark would ignite. So an aircraft or a tanker is BONDED to the fuelling equipment with a conducting cable before any fuel moves, and both are connected to earth. The cable is not there to carry fuel or power. It is there to make sure that no part of the arrangement can be at a different potential from any other part, so there is nothing for a spark to jump across.

The same reasoning explains the other dangers on the list. A person who becomes charged walking across a nylon carpet can receive a shock on touching a metal door handle — unpleasant rather than harmful, but in a hospital operating theatre or a factory handling flammable solvents it is a serious matter, which is why anti-static flooring is used. Refuelling a car with the engine running, or getting back into the car and out again mid-fill, is discouraged for exactly this reason.

Think of it like water building behind a dam with no outlet

Charge accumulating on an insulator is water rising behind a wall with no spillway: nothing happens for a long time, and then it goes over all at once and violently. Earthing is cutting a channel at the bottom — the water never rises far, because it is always draining, and the sudden release can never happen. Notice that earthing does not remove the source. Fuel still flows and friction still separates charge; the charge is simply led away as fast as it appears. That is why the bonding cable is attached BEFORE the fuelling starts and removed afterwards, rather than being used to discharge something that has already built up.

Now the uses, which all depend on the fact that charged objects attract uncharged ones and that a fine spray of charged droplets spreads itself out. A PHOTOCOPIER works by giving a plate an electrostatic charge, then projecting an image of the page onto it — the light discharges the plate wherever the page was white, leaving charge only where the print was black. Charged black toner powder is attracted to those charged areas, transferred onto paper, and melted onto it by a hot roller.

The three uses named by the specification

1. PHOTOCOPIER: a charged plate is exposed to an image of the page; light discharges it where the page was white; charged toner powder sticks to the charged areas that remain; the toner is transferred to paper and melted onto it by a hot roller.
2. INKJET PRINTER: the ink is broken into tiny droplets which are given an electrostatic charge, then deflected by charged plates as they fly past. Changing the voltage on the plates steers each droplet to the right place on the paper.
3. ELECTROSTATIC PAINT SPRAYING: the paint droplets are charged, so they repel each other and spread into an even mist rather than clumping — and the object being painted is given the opposite charge, so the paint is attracted to it and wraps round the back as well. Very little is wasted.

It is worth noticing how similar the useful and dangerous cases are. In both, charge is deliberately or accidentally separated; in both, that charge attracts something. The whole difference is whether the situation was designed. A paint sprayer charges droplets on purpose and controls where they land; a fuel hose charges the fuel by accident and has nowhere to put the charge. The physics does not distinguish between them at all.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

Statement 2.27 — the danger, and the answer to write

1. Friction between the moving surfaces transfers electrons, so charge builds up.
2. The surfaces are insulators, so the charge cannot flow away and continues to accumulate.
3. Eventually the charge is large enough to produce a spark across a gap.
4. The spark can ignite fuel vapour, dust or powder, causing a fire or an explosion.
5. The remedy is to earth or bond the objects with a conductor, so the charge flows away continuously and never builds up.

Statement 2.28 — the uses, each with the electrostatic reason

• PHOTOCOPIER — a charged plate is discharged by light where the page was white; charged toner is attracted to the charged areas that remain
• INKJET PRINTER — droplets are charged and then deflected by charged plates, so changing the plate voltage steers each droplet to the right place
• PAINT SPRAYING — charged droplets REPEL each other into an even mist, and are ATTRACTED to an oppositely charged object, wrapping round the back
• In every case: like charges repel and unlike charges attract, and a charged object attracts an uncharged one

Learn this definition · Earthing (in electrostatics)

Connecting a charged or chargeable object to the ground with a conductor, so that charge flows away continuously and cannot build up enough to cause a spark.

Learn this definition · Spark (electrostatic discharge)

The sudden movement of charge across a gap, which happens when enough charge has built up to make the air between conduct. It releases heat, light and sound, and can ignite vapour or dust.

The same physics, wanted and unwanted

Two things earthing is doing

A. IN A FUEL TANKER it prevents charge from EVER building up, by giving it a continuous path to the ground before a spark becomes possible.

B. IN A MAINS APPLIANCE it carries a large fault current away from a person and makes the fuse melt. The path is the same idea; the job is different.

Model answer [4 marks]

Explain why an aircraft is connected to the fuel tanker by a conducting cable before refuelling begins. [4]

As the fuel flows through the hose, friction transfers electrons between the fuel and the hose, so electrostatic charge builds up. Because the fuel and the hose are insulators, this charge cannot flow away and continues to accumulate. If it becomes large enough it can cause a spark across a gap, and a spark near fuel vapour could ignite it and cause an explosion. The conducting cable connects the aircraft and the tanker to each other and to earth, so any charge flows away continuously through the conductor and never builds up enough for a spark to occur.

Model answer [4 marks]

Explain how electrostatic charge is used in spraying paint onto a car body. [4]

The paint droplets are given the same electrostatic charge as they leave the nozzle. Like charges repel, so the droplets push each other apart and spread into a fine, even mist rather than clumping together. The car body is given the opposite charge, so the droplets are attracted to it. Because they are attracted to the metal rather than simply travelling in straight lines, the paint reaches the sides and even the back of the body, giving an even coat and wasting very little paint.

Not this: The bonding cable on a fuel tanker is there to discharge the static that has already built up.

This: It is attached BEFORE fuelling starts, so that charge never builds up in the first place. It provides a continuous path to earth while the fuel is flowing, which is when the charge is being generated.

Mark-losing trap. For dangers, name the SPARK and what it ignites — fuel vapour, dust or powder.

Mark-losing trap. The remedy is EARTHING with a CONDUCTOR, connected before the process starts.

Mark-losing trap. For paint spraying, give BOTH effects: droplets repel each other, and are attracted to the object.

Mark-losing trap. Explain everything by ELECTRON movement — that is what statement 2.26 is asking for.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · State [1 mark] — What is done to a fuel tanker to prevent electrostatic charge from building up during refuelling?
2. Grade 7 · Explain [2 marks] — In electrostatic paint spraying, the paint droplets are all given the same charge. Explain why this gives an even coat.
3. Grade 8 · Explain [5 marks] — Select every statement that belongs in a full-mark explanation of why refuelling an aircraft can be dangerous if it is not earthed.
4. Grade 9 · Describe [5 marks] — Select every statement that belongs in a full-mark description of how a photocopier uses electrostatic charge to copy a page.
5. 9+ · Analyse [6 marks] — A factory handling flour has an explosion. An investigator finds that the plastic ducting carrying the flour was not earthed. A manager says: 'Flour is not flammable like petrol, so static cannot have been the cause.' Select every statement that belongs in a full-mark analysis.

The people behind this science

Two ways into the same idea — the one who worked with discharges deliberately, at enormous scale, and the one who found that charge sits on the outside, and knew what it implied. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Nikola Tesla — the one who worked with discharges deliberately, at enormous scale

Tesla spent years generating potentials of millions of volts and watching what they did to the air around them, so he is the person on this page who has looked hardest at the event it turns on. A spark is the air itself briefly becoming a conductor, and he studied exactly where that threshold lies, how discharges creep along surfaces and how they can be steered. His Colorado Springs work in 1899 produced discharges tens of metres long — the same physics as a crackle from a jumper, differing only in scale.

• “What is actually happening in the air when a spark jumps?”
• “How much charge has to build up before the air gives way?”
• “Why does a discharge choose one path rather than another?”
• “What did you learn from making artificial lightning at Colorado Springs?”
• “How would you protect something from a discharge you could not prevent?”

Joseph Priestley — the one who found that charge sits on the outside, and knew what it implied

In 1767 Priestley followed up an observation of Franklin's: cork balls hung inside a charged metal cup were not affected at all, though the same cup attracted them strongly from outside. Priestley reasoned, by analogy with the known result that gravity vanishes inside a hollow sphere, that the electrical force must also fall off as the square of the distance — a genuine piece of theoretical inference, made years before Coulomb measured it. It also explains why a metal enclosure shields whatever is inside it, which is how sensitive equipment and aircraft are protected from discharges.

• “Why is there no charge on the inside of a charged hollow container?”
• “How did you reason from gravity to the force between charges?”
• “What did Franklin's cork-ball observation actually show?”
• “Would something inside a metal box be safe from a lightning strike?”
• “How much can you conclude from an experiment where nothing happens?”

Then defend it

On Incandio a lesson is not finished when the questions come out right. You teach the idea back to Ember, an AI apprentice who asks the awkward question, and then you argue it against Benjamin Franklin in a structured debate marked against descriptors you can read before you enter. Learn it, teach it, then defend it — all three happen on this page once the app loads.

Carry on through the course

• Previous lesson: Static Electricity
• Next lesson: What a Wave Is
• Charge and Current — What is actually moving in a wire, how fast it is really going, and why the arrows on every circuit diagram point the wrong way.
• Resistance and Ohm's Law — What slows the electrons down, the one equation that ties the whole topic together, and when it stops being true.
• Series and Parallel Circuits — Two ways of joining components, and why every building in the world is wired one of them.
• Current–Voltage Graphs, LDRs and Thermistors — The shapes four components make on a graph, and two resistors that deliberately refuse to stay the same.
• Voltage as Energy per Charge — What a volt actually is — and why knowing that turns three separate equations into one idea.
• All of Physics · Incandio Science