A lorry carrying fuel through a dry desert region can build up a large static charge as it travels. Before connecting a fuel pipe to a storage tank, the driver attaches a metal wire between the lorry and the tank. Explain why this is necessary to prevent a spark.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Fuel tanker lorries can accumulate static charge whilst travelling due to friction between tyres and the road surface, and between fuel and the inside of the tank. A spark near flammable fuel can be extremely dangerous.
Model answer (4 marks)
Friction between the tyres and the road, and between the fuel and the tank, transfers electrons and leaves the lorry charged.
The lorry and the storage tank can therefore be at different electrical potentials.
A metal wire connects the two, allowing electrons to flow until their charges are equalised.
If the wire were absent, the excess charge could discharge suddenly across the air gap as a spark, which could ignite the fuel.
The lorry and the storage tank can therefore be at different electrical potentials.
A metal wire connects the two, allowing electrons to flow until their charges are equalised.
If the wire were absent, the excess charge could discharge suddenly across the air gap as a spark, which could ignite the fuel.
Examiner tips
- Use the word ‘friction’ and ‘electrons’ to show cause. Mention ‘different potentials’ to explain the danger. State that the wire equalises charge. Explain that a spark would ignite the fuel.
Common mistakes
- Saying the wire is ‘good’ without explaining charge equalisation. Forgetting to mention the spark’s danger to the fuel.
Mark scheme (4 marks)
- Friction causes electrons to transfer, building up charge on the lorry
- The lorry and tank may be at different electrical potentials / have different charges
- The metal wire allows charge / electrons to flow between the lorry and tank, equalising their charge
- Without the wire, charge could discharge suddenly across the gap as a spark, which could ignite the fuel
Key terms in this question
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Static and charge questions
- A student rubs a plastic ruler with a dry cloth. The ruler becomes negatively ch…
- A balloon is rubbed against a woollen jumper. The balloon then sticks to a wall …
- A person walks across a nylon carpet wearing rubber-soled shoes. When they then …
- A technician working in a microchip factory must wear a special wristband that c…