Electric Charge
4 marks · EasyDuring refuelling, an aircraft is connected to earth with a metal cable. At the same time, a gold leaf electroscope is used to show the effect of bringing a charged rod near its metal plate.
Explain why an aircraft is earthed before refuelling.
Describe what happens to the gold leaf if a positively charged rod is brought close to the metal plate of the electroscope.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The aircraft is earthed so charge can flow away safely, preventing sparks that could cause explosions or fires during refuelling.
(b) The leaf rises. Negative charges are attracted to the metal plate, leaving the rod and leaf with like charges, so they repel each other.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States earthing allows charge to flow away or be neutralised.
A1 (a) · 1 mark · Explains this prevents a dangerous spark (explosion/fire risk).
M2 (b) · 1 mark · Explains that like charges on the leaf and rod cause repulsion.
A2 (b) · 1 mark · Correctly describes the leaf rises or deflects.
Worked solution
a) Earthing the aircraft provides a path for excess static charge to flow safely away to the ground. This prevents sparks that could ignite fuel vapours.
b) When a positively charged rod is brought near the plate, negative charges are attracted to the plate and the gold leaf and stem become positively charged. The leaf rises because both the stem and leaf have the same charge and so repel each other.