Static electricity and electric fields (physics only) – GCSE Physics exam questions with mark scheme

1Grade 1–3FoundationTriple only4 marks

A student rubs a polythene rod with a woollen cloth. The rod becomes negatively charged.

(a) Name the particles that are transferred when the rod is rubbed. [1]

(b) Complete the sentence.

The particles move from the ____________ to the ____________. [1]

(d) Another student says: 'The cloth becomes charged because positive charges move onto it from the rod.'

Explain why this student is wrong. [1]

(a) electrons do not accept electricity / charge / negative charges alone; reject protons(1)
(b) (woollen) cloth to (polythene) rod both needed, in this order(1)
(c) positive ignore any reference to the size of the charge unless it is stated to be different from the rod's(1)
(d) positive charges / protons cannot move (as they are in the nucleus) and the cloth is positive because it has lost electrons allow only electrons are transferred, so the cloth loses electrons(1)
Answer: (a) electrons (b) cloth → rod (c) positive (d) protons cannot move; the cloth is positive because it has lost electrons.
Examiner tip: Only electrons ever move when insulators are rubbed – any answer that has positive charges moving gets no credit.

2Grade 1–3FoundationTriple only3 marks

Two identical balloons are each rubbed on the same woollen jumper. Both balloons become negatively charged.

The balloons are hung from the same point by threads. The diagram shows the balloons after they are released.

(a) Explain why the balloons hang apart from each other. [2]

(b) The balloons are not touching. What type of force acts between them? [1]

(a) the balloons have the same (type of) charge / both are negative allow like charges(1)
(a) like charges repel (so they push each other apart) allow same charges repel; do not accept 'they repel' without reference to the charges for this mark(1)
(b) non-contact (force) allow electrostatic (force); ignore 'repulsive' on its own(1)
Answer: (a) both balloons are negatively charged; like charges repel. (b) a non-contact (electrostatic) force.
Examiner tip: 'They repel' is not enough – say why: the charges are the same type, and like charges repel.

3Grade 4–5Triple only3 marks

An acetate rod is rubbed with a cloth. After rubbing, the rod has a charge of $+6.4 \times 10^{-9}$ C.

(a) Has the rod gained or lost electrons? Give a reason for your answer. [1]

(b) The charge on one electron is $-1.6 \times 10^{-19}$ C.

Calculate the number of electrons that moved between the rod and the cloth. [2]

(a) lost (electrons) and because the rod is (now) positive / has more protons than electrons no mark for 'lost' alone(1)
(b) $n = \dfrac{6.4 \times 10^{-9}}{1.6 \times 10^{-19}}$ ignore minus signs(1)
(b) $4.0 \times 10^{10}$ allow 40 000 000 000; an answer of $4 \times 10^{10}$ scores 2 marks; a negative answer scores 1 mark(1)
Answer: (a) lost electrons, because the rod is positive (b) $4.0 \times 10^{10}$ electrons
Examiner tip: The number of electrons cannot be negative – divide the sizes of the charges and ignore the sign.

4Grade 6–7HigherTriple only5 marks

A student investigates how the force between two small charged spheres depends on the distance between their centres.

The table shows her results.

Distance between centres in cm	Force in mN
2.0	7.2
3.0	3.2
4.0	1.8
6.0	0.80

(a) Describe how the force changes as the distance increases. [1]

(b) Use data from the table to show that when the distance doubles, the force becomes one quarter of its value. [2]

(d) Explain, in terms of the electric field, why the force is smaller when the spheres are further apart. [1]

(a) the force decreases (as distance increases) allow the force decreases by smaller amounts each time / not proportionally; do not accept 'inversely proportional'(1)
(b) one correct pair compared, e.g. 2.0 cm → 4.0 cm: 7.2 mN → 1.8 mN or 3.0 cm → 6.0 cm: 3.2 mN → 0.80 mN(1)
(b) shown to be a factor of 4, e.g. $7.2 \div 1.8 = 4$ or $1.8 = 7.2 \div 4$ allow $3.2 \div 0.80 = 4$(1)
(c) 0.45 (mN) (1.8 ÷ 4)(1)
(d) the (electric) field (of each sphere) is weaker further from the (charged) sphere allow converse: field is strongest close to the sphere; do not accept 'the charge is weaker'(1)
Answer: (a) the force decreases (b) e.g. 2.0 → 4.0 cm: 7.2 ÷ 1.8 = 4 (c) 0.45 mN (d) the field is weaker further from a charged sphere.
Examiner tip: 'Show that' needs actual numbers from the table and the division that gives 4 – just saying 'it goes down by a quarter' scores nothing.

5Grade 6–7Triple only6 marks

An aircraft is refuelled from a fuel tanker. The fuel flows quickly through a long rubber hose from the tanker into the aircraft.

Before refuelling starts, a metal cable is connected from the aircraft to the ground.

Explain why charge can build up during refuelling, why this is dangerous, and how the metal cable prevents the danger. [6]

fuel rubs against the inside of the hose / pipes (friction)(1)
electrons are transferred between the fuel and the hose(1)
one becomes negatively charged and the other becomes (equally) positively charged(1)
charge is carried with the fuel into the aircraft, so the aircraft becomes charged(1)
the aircraft is insulated from the ground (rubber tyres) so the charge cannot escape and builds up(1)
the potential difference between the aircraft and the ground / tanker increases(1)
a (strong) electric field forms around the charged aircraft, strongest close to it(1)
when the field is strong enough, charge jumps across the air as a spark(1)
a spark could ignite fuel vapour, causing a fire / explosion(1)
the metal cable is a conductor (connected to earth)(1)
electrons can flow along the cable between the aircraft and the ground(1)
so charge does not build up / the aircraft is discharged, so no spark is produced(1)

Level	Marks	What it looks like
Level 3	5–6	A detailed, coherent explanation covering all three parts: how charge builds up (in terms of electron transfer by friction and insulation from the ground), why a spark is dangerous, and how the cable lets charge flow to or from earth. Reasoning is linked in a logical chain.
Level 2	3–4	A clear explanation of at least two of the three parts, or all three with limited detail, e.g. friction causes charge to build up, a spark could ignite the fuel, the cable earths the aircraft. Some steps may be missing or not linked.
Level 1	1–2	Simple relevant statements with little linking, e.g. 'the fuel rubbing makes static' or 'a spark could cause an explosion' or 'the cable earths it'.
0	0	No relevant content.

Answer: Friction between fuel and hose transfers electrons, charging the fuel and so the aircraft; the rubber tyres insulate it, so charge and the pd to earth build up. A strong field can produce a spark that ignites fuel vapour. The metal cable lets electrons flow to/from earth so charge never builds up and no spark forms.
Examiner tip: Top-band answers link three things in a chain: electron transfer by friction → build-up of charge (and field) → spark igniting vapour, then explain the cable as a conducting path to earth.

6Grade 4–5Triple only4 marks

A child slides down a plastic slide. At the bottom, the child's hair stands on end and the hairs spread out away from each other.

(a) Explain why the child's hairs stand on end and spread apart. [3]

(b) The child then goes down a metal slide that is connected to the ground. The child's hair does not stand on end.

Suggest why. [1]

(a) friction / rubbing between the child (or clothes) and the slide transfers electrons allow electrons move between the child and the slide; reject positive charges / protons move(1)
(a) (so) each hair gains the same type of charge allow all the hairs become positive or all become negative(1)
(a) like charges repel, so the hairs push away from each other (and from the head) do not accept 'the hairs repel' with no reference to like charges(1)
(b) metal is a conductor, so electrons / charge flow to or from the ground / earth (so no charge builds up on the child) allow the charge is earthed; ignore 'the metal does not make static'(1)
Answer: (a) Rubbing transfers electrons, so every hair gets the same type of charge; like charges repel so the hairs push apart. (b) The earthed metal conducts, so charge flows away to the ground and does not build up.
Examiner tip: The key idea is that every hair has the SAME charge – that is why they push away from each other.

7Grade 4–5Triple only4 marks

A small ball hangs from an insulating thread. The ball is positively charged.

A negatively charged rod is held near the ball. The diagram shows the result.

(a) Explain why the thread is no longer vertical. [2]

(b) The rod is moved closer to the ball, without touching it.

Describe and explain what happens to the angle of the thread from the vertical. [2]

(a) the ball and the rod have opposite / unlike charges allow positive and negative(1)
(a) unlike charges attract, so (a force pulls) the ball (is pulled) towards the rod(1)
(b) the angle (from the vertical) increases allow the ball moves further towards the rod(1)
(b) (because) the force (of attraction) increases as the distance decreases allow the ball is in a stronger part of the rod's electric field(1)
Answer: (a) The charges are opposite and unlike charges attract, pulling the ball towards the rod. (b) The angle increases because the attractive force is bigger when the distance is smaller.
Examiner tip: In (b) give a direction of change for the angle AND link the larger force to the smaller distance.

8Grade 6–7Triple only4 marks

The diagram shows the positively charged metal dome of a Van de Graaff generator. An earthed metal sphere is moved slowly towards the dome.

No spark is seen until the gap between the dome and the sphere becomes small.

(a) Explain, in terms of the electric field, why a spark only jumps across the gap when the gap is small. [3]

(b) State the direction in which electrons move when the spark jumps. [1]

(a) the charged dome has an electric field around it which is strongest close to the dome allow the field is weaker further from the dome(1)
(a) as the sphere moves closer / the gap decreases, the electric field (strength) in the gap increases(1)
(a) when the field is strong enough, the air (molecules) is ionised / electrons are pulled from the air, so the air conducts (and charge flows as a spark) allow air becomes a conductor; allow the air breaks down(1)
(b) from the (earthed) sphere to the dome allow from earth / the ground to the dome; reject from the dome to the sphere(1)
Answer: (a) The field around the dome is strongest close to it; as the gap shrinks the field in the gap increases until it is strong enough to ionise the air, which then conducts and a spark jumps. (b) From the earthed sphere to the dome.
Examiner tip: A positive dome has LOST electrons, so electrons flow TO it from earth – many students reverse this.

9Grade 6–7Triple only5 marks

A person walks across a nylon carpet and becomes negatively charged.

When the person's finger gets close to a metal door handle, a spark jumps between the finger and the handle.

(a) In the spark, a charge of 0.48 μC flows in a time of 0.16 μs.

Calculate the average current in the spark. [3]

(b) State the direction in which electrons flow in the spark. [1]

Explain why. [1]

(a) $0.48 \times 10^{-6} = I \times 0.16 \times 10^{-6}$ allow $Q = It$ correctly substituted with consistent units, e.g. $0.48 = I \times 0.16$(1)
(a) $I = \dfrac{0.48 \times 10^{-6}}{0.16 \times 10^{-6}}$(1)
(a) 3.0 (A) an answer of 3 (A) scores 3 marks; an answer of $3 \times 10^{-6}$ or $3 \times 10^{6}$ scores 2 marks (one prefix not converted)(1)
(b) from the finger / person to the handle allow from the person to earth(1)
(c) the person is no longer charged / the (excess) electrons have already flowed away (to earth) allow the person has been discharged; ignore 'the charge has been used up'(1)
Answer: (a) 3.0 A (b) from the finger to the handle (c) the excess electrons have already flowed away, so the person is no longer charged.
Examiner tip: Both quantities are in 'micro', so the prefixes cancel – but if you convert only one of them the answer is out by a factor of $10^{6}$.

10Grade 4–5Triple only4 marks

The diagram shows an isolated, positively charged metal sphere.

(a) Draw the electric field pattern around the sphere. [2]

(b) State where the electric field is strongest. [1]

(c) The sphere is replaced by an identical sphere with a negative charge. Describe how the field pattern would be different. [1]

(a) at least four straight lines, radial (at right angles to the surface), spread evenly around the sphere lines must start on the surface of the sphere; ignore line length; lines must not cross(1)
(a) arrows on the lines pointing away from the sphere arrows must all be consistent; do not award if any arrow points inwards(1)
(b) close to / at the surface of the sphere allow nearest the sphere; do not accept 'in the middle of the sphere'(1)
(c) the arrows / direction of the field would point towards the sphere (the shape is the same) allow field lines point inwards(1)
Answer: (a) evenly spaced radial lines from the surface with arrows pointing outwards (b) close to the sphere (c) the field lines would point inwards, towards the sphere.
Examiner tip: Field lines start on the surface and point away from a positive charge – arrows are needed for the second mark.

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