Static electricity (physics only) static charge and electric fields

SPEC 8463 • 4.2.5 • PAPER 1 ⭐

⚡ PHYSICS-ONLY

Static Electricity

Module 2's last lesson. The worst-performing topic in Module 2 — three Jun 2024 questions where the top mark eluded most students. Lock the mark-scheme wording in here.

What This Lesson Covers

Part A — 4.2.5.1

Static charge

Charging by friction (electrons only)

Like/unlike charge forces

Sparking

Part B — 4.2.5.2

Electric fields

The field concept

Drawing the field pattern

Force at a distance

Physics-only — combined-science skip this

This content is on AQA Physics 8463 Paper 1 only. Combined Science Trilogy students do not study static electricity.

Why this is high-stakes

Jun 2024 Paper 1H Q4 was the worst-performing question in Module 2 — only 10% scored 3/3 on the hair-stands-on-end explanation, and only 8% correctly defined an electric field. Mark-scheme wording is everything here.

Charging by Friction — Electrons Only

When two insulating materials are rubbed together, they become electrically charged. Friction transfers electrons — and only electrons — from one surface to the other.

Material that LOSES electrons

Becomes POSITIVELY charged

Material that GAINS electrons

Becomes NEGATIVELY charged

Equal and opposite

The two materials end up with equal magnitudes of opposite charge. If one gains 1000 electrons, the other has lost 1000 electrons.

Protons and neutrons NEVER transfer

Protons sit inside atomic nuclei — they don't move freely during friction. Neutrons don't carry charge anyway. Only electrons move. State this explicitly when explaining static charging.

Why "insulating" materials specifically?

The spec says "certain insulating materials" — not conductors. In a conductor, free electrons can flow easily, so any charge picked up by friction immediately flows away to earth (through whatever the conductor touches). In an insulator, electrons can't flow freely, so the charge stays on the surface where the rubbing happened — building up as visible static.

Examiner Alert — Charging Explanations

Jun 2024 Paper 1H · Q04.1

"Explain why the student's hair stands up on end" — 3 marks, after touching a negatively-charged metal dome. Only 10% scored 3/3. 32% scored just 1 mark.

"Statements about transfer of positive electrons or protons or even neutrons were commonly seen. Students struggled to understand that when you are in contact with a charged object, you have the same charge as that object." — AQA Examiner Report, Jun 2024 Paper 1H

Two killer errors

"Protons / neutrons transferred" — only electrons move. Protons are stuck in nuclei.

"The negative dome makes the person positive" — wrong. Touching a charged object gives the person the same sign of charge. Mark scheme explicitly rejects "student becomes positive" for the first two marks.

Forces Between Charged Objects

When two charged objects are brought close to each other, they exert a force on each other without touching — a non-contact force.

Same / like charges

+ ↔ +

− ↔ −

REPEL

Different / unlike charges

+ → ← −

ATTRACT

Non-contact force

The charges aren't touching, but they still exert forces on each other across space. The force acts through a region of space called the electric field (next half of the lesson).

3-Mark PEE — Hair Stands On End

The Jun 2024 Q4.1 model answer. Three marks, three clauses. Use the exact mark-scheme wording.

"Explain why a student's hair stands up on end after touching a negatively-charged metal dome."3 marks

Model answer

Electrons are transferred to the student (from the dome). (1 mark)

Her hair is now negatively charged — each hair carries the same negative charge. (1 mark)

Like charges repel, so the hairs push apart and stand on end. (1 mark)

If you call the student "positively charged"

Per the Jun 2024 mark scheme: "If a student said that the student was positively charged they could not score mark points 1 and 2, but they could still score mark point 3 if they said 'like / same charges repel'." Get the sign right or lose 2/3.

What is an Electric Field?

A charged object creates an electric field around itself. Any other charged object placed in this field experiences a force.

Mark-scheme verbatim — memorise word for word

An electric field is the region around a charged object where another charged object would experience a force.

Mark-scheme alternatives accepted

"area" or "space" instead of "region"

"particle" instead of "object"

"experiences repulsion or attraction" instead of "force"

"charged particles or ions" as examples of "charged objects"

Why the field concept matters

The field explains action at a distance — how charges affect each other without touching. The field is the "mechanism" by which the non-contact force is transmitted.

Examiner Alert — Defining the Field

Jun 2024 Paper 1H · Q04.2 — the 8% question

"Define an electric field" — 1 mark. Only 8% of students scored this single mark. The lowest scoring single-mark question in the topic.

"An answer of 'the area / space / region where an electron experiences a force' was creditworthy as were other examples of charged particles or ions. 'The area where other charged particles experience repulsion or attraction' was also creditworthy. Neither of these examples were seen often." — AQA Examiner Report, Jun 2024 Paper 1H

Why students fail this

Most students describe what a field does, not what it is. Mark scheme wants the phrase "region/area/space where another charged object/particle experiences a force". Three components needed:

A region/area/space (what type of thing it is)

Around a charged object

Where another charged object/particle experiences a force

Drawing the Field — Spec-Required Diagram

The spec requires you to draw the electric field pattern for an isolated charged sphere. Radial arrows show the field direction.

Radial pattern, equally spaced arrows. Outward for positive (direction a positive test charge would move). Inward for negative.

Drawing for marks

Use a ruler for straight lines

Arrows must point in the correct direction (out for +, in for −)

Distribute lines evenly around the sphere

Lines must not cross each other

Field Strength Decreases With Distance

The electric field is strongest close to the charged object and weakens with increasing distance.

Close to the sphere

Field is STRONGEST

Force on a second charged object is greatest here.

Far from the sphere

Field is WEAKER

Force is smaller; eventually negligible.

Force as objects get closer

The force between two charged objects gets stronger as the distance between them decreases. This is the spec wording — use exactly this phrasing in answers.

Jun 2024 Q4.3 — answer the question asked

This was a "what happens to field strength as you move away?" question worth 1 mark. 92% scored, but many wrote "as you get closer, field strength increases" — true, but answering the inverse question. Stick to the direction the question asked: as you move away, it decreases.

Sparking — Spec-Required

The spec explicitly requires you to describe sparking by rubbing surfaces and explain it using the field concept.

How a spark forms

Two surfaces are rubbed → electrons transfer → one surface becomes highly charged.

The pd between this surface and a nearby earthed (or oppositely-charged) object becomes very large.

The electric field in the air gap becomes strong enough to ionise the air — pulling electrons off air molecules.

The ionised air conducts, allowing electrons to jump across the gap as a spark — a brief flow of charge.

Factors that increase spark distance

Higher pd between the objects → stronger field → can ionise air over a longer gap

More charge on the object → produces a higher pd → same effect as above

Lower electrical resistance of air (e.g. ionised or more conductive air) → sparks pass more easily

Jun 2024 Q4.5 — multiple choice on this

80% of students identified the correct factor that would increase spark distance. The tricky options test whether you understand which physical quantity directly enables longer sparks. Reason through the field-and-ionisation mechanism, not memory.

E = Q × V — Now With μC

Static-electricity calculations often use the E = Q × V equation from lesson 2.09, but with charges in microcoulombs (μC) — very small charges typical of static buildup.

E = Q × V

μC → C conversion

1 μC = 1 × 10⁻⁶ C = 0.000001 C

Always convert μC to C before substituting. Substituting μC directly gives an answer wrong by a factor of one million.

Typical numbers

Static-charge values are tiny (μC range), but pds can be huge (tens or hundreds of kV). The energy stored is small (J range) but the field can be intense enough to spark.

Examiner Alert — μC Conversion

Jun 2024 Paper 1H · Q04.4

An E = QV calculation with charge given in μC. 36% scored 4/4; 56% scored 3/4. The drop-off: not converting μC to C.

"Some students did not convert, or incorrectly converted, the unit of charge and scored 3 marks. Some students incorrectly converted the unit for charge and also spuriously converted the energy by multiplying or dividing by a power of ten. These students made two mistakes." — AQA Examiner Report, Jun 2024 Paper 1H

Defence

Convert μC to C in standard form: e.g. 2 μC = 2 × 10⁻⁶ C. Write it out — don't try to do it mentally.

Don't convert the energy. If E is given in joules, leave it in joules. Only convert the unit that needs converting.

Show working: write the conversion step explicitly. Mark schemes credit partial working.

Practice — E = QV with μC

A charged dome stores a charge of 5.0 μC. The energy stored is 1.0 J. Calculate the potential difference between the dome and earth.4 marks

E

Equation: E = Q × V, so V = E ÷ Q

C

Convert: 5.0 μC = 5.0 × 10⁻⁶ C (1 mark)

S

Substitute: V = 1.0 ÷ (5.0 × 10⁻⁶) (1 mark)

U

Units: volts (V)

A

V = 200 000 V (= 200 kV) (2 marks for correct rearrangement and answer)

!

Common error: not converting μC. Using Q = 5.0 directly gives V = 0.2 V — wrong by a factor of one million.

Weak vs Strong Answers

Two classic Jun 2024 questions. Compare the responses examiners see most often vs the ones that score full marks.

Q: "Define an electric field."1 mark

Weak (0/1)

"An electric field is what surrounds a charge."

Doesn't say what it IS or what HAPPENS in it. No mark.

Strong (1/1)

"The region around a charged object where another charged object experiences a force."

Q: "Explain why the student's hair stands up."3 marks

Weak (1/3)

"The dome is negative so the student becomes positive. The opposite charges make her hair stand up."

Wrong charge sign. "Opposite charges attract" wouldn't make hair stand up anyway.

Strong (3/3)

"Electrons are transferred to the student. Her hair is negatively charged. Like charges repel, so the hairs push apart."

Q: "What is an electric field?" — common misconception

Weak (0/1)

"An electric field is the area around any object."

Wrong — only charged objects produce electric fields. A neutral object has no field around it.

Strong (1/1)

"The region around a charged object where another charged object would experience a force."

Mark-Scheme Language

The exact phrases AQA mark schemes credit. Use these verbatim.

ConceptMark-scheme phrase

Charging mechanism"Electrons are transferred"

Charge gained"Material gains electrons → becomes negatively charged"

Charge lost"Material loses electrons → equal positive charge"

Force rules"Like / same charges repel; different / opposite charges attract"

Electric field definition"The region around a charged object where another charged object experiences a force"

Field strength variation"Field strength decreases with distance from the charged object"

Force variation"The force gets stronger as the distance between objects decreases"

Recap

Static charge (4.2.5.1)

Electrons transfer; loser is + and gainer is −. Like repel, unlike attract. Sparking via field ionising air.

Electric fields (4.2.5.2)

Region around a charged object where another charge feels a force. Radial pattern. Strongest near, weaker far.

The three killer errors to avoid

1

"Protons transferred" — only electrons move.

2

Wrong sign of charge on a person touching a charged object — they have the same sign as the object.

3

Forgetting to convert μC to C in E = QV calculations.

🎉 Module 2 Complete!

You've finished the Electricity module — 10 lessons covering circuits, equations, mains, power, energy transfers, the National Grid, and now static. Module 3 (Particle Model) up next.

Checkpoint

You can now:

Describe charging by friction — electrons only transferred.

Identify which object becomes positively and which becomes negatively charged.

State the rule: like charges repel, unlike charges attract .

Recognise that a person touching a charged object has the same charge as it.

Define an electric field using mark-scheme wording.

Draw the field pattern for an isolated charged sphere (radial arrows).

Explain how the field varies with distance (strongest close, weaker far).

Explain sparking via the field-ionises-air mechanism.

Apply E = QV with μC → C conversion.

Next module

Module 3 — Particle Model of Matter. Density, changes of state, internal energy, specific heat capacity, specific latent heat, and gas behaviour. Six lessons (3.01 through 3.06), starting with density and RP5.