Q3 Read the following passage and answer the accompanying questions. A group of teachers were discussing the hazards of static electricity over coffee in their school staffroom. The English teacher asked the physicist: ‘Why does one earth aircraft during refuelling, but not cars at a petrol station?’
The physicist replied that both the plane and the car are earthed; the car’s fuel tank and filler neck are bonded to the car chassis and the tyres are loaded with carbon to make them electrically conductive.
The English teacher replied: ‘Then why the extra precautions when refuelling aircraft and F1 race cars?’ The reply came from the economics teacher: ‘All to do with scale; more fuel, less time, more people and more expensive vehicles.’
A maths teacher, who overheard the conversation, thanked the physicist and recounted a story. ‘I had been pondering as to why my car occasionally zapped me or my wife as we got out of it. I had assumed that either one of us was discharging the car. I always let her get out first so she would get the shock, but that didn’t always work. Sometimes I’d get zapped too. I now realise that we were not discharging the static build-up on the car through ourselves but discharging static on ourselves through the car.’
The physicist suggested:‘Next time, open the car door, touch any metal part of car and only then put your feet on the ground; but don’t tell your wife!’
(a) Explain why all the charge resides on the outside of the car.
(Adapted from a staffroom conversation) (7)
(b) Describe an experiment to demonstrate that total charge resides on the outside of a conductor.
(c) Give two applications that make use of the fact that charge remains on the outside of the hollow conductor.
(d) How does charge build up on the people inside the car?
(e) Why does touching the metal part of the car before exiting the car mean that the passenger will not get a shock?
(f) A strong electric field would build up around the car during travel if it weren’t earthed during its journey. What is meant by electric field strength?
(14)
(7) (7)
(7) (7) (g) Give one other safety hazard caused by static electricity and describe a precaution taken against it. (7)
