2.13 Static charge
9 exam questions worth 21 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which particles are transferred when a polythene rod is rubbed with a cloth?
Choose one answer.
Correct Not quite: the answer is Electrons
Mark scheme
A: electrons
Model answer
Electrons (A).
A polythene rod is rubbed with a cloth and becomes negatively charged. Explain how.
Mark scheme
friction (between the rod and cloth) causes electrons to be transferred (1); electrons move from the cloth to the rod (1); the rod gains extra negative charge (and the cloth is left positive) (1)
Model answer
Rubbing causes electrons to be transferred from the cloth to the rod. The rod gains electrons, so it has an overall negative charge, and the cloth, which has lost electrons, is left with a positive charge.
State what happens when (a) two negatively charged rods and (b) a positively charged rod and a negatively charged rod are brought close together.
Mark scheme
(a) they repel (1); (b) they attract (1)
Model answer
(a) The two negative rods repel each other. (b) The positive and negative rods attract each other.
A charged balloon sticks to a wall, even though the wall has no overall charge. Explain why.
Mark scheme
the charge on the balloon causes the electrons in the wall to move / the surface of the wall nearest the balloon gets the opposite charge (1); unlike charges attract, so the balloon is attracted to the wall (1)
Model answer
The charge on the balloon pushes electrons in the wall away from its surface, so the surface nearest the balloon has the opposite charge. Unlike charges attract, so the balloon sticks to the wall.
A person walks across a nylon carpet and then gets a small shock when touching a metal door handle. Explain why.
Mark scheme
friction between shoes and carpet transfers electrons so the person becomes charged (1); the charge cannot flow away through the insulating shoes, so it builds up, giving a large potential difference between the person and the door handle (1); charge flows through the air / person as a spark when they touch the handle (1)
Model answer
Friction between the shoes and the carpet transfers electrons, so the person becomes charged. The charge cannot escape through insulating shoes, so it builds up until there is a large potential difference between the person and the handle. When the person touches the handle, charge flows to the handle, giving a shock.
Explain why an aircraft is earthed while it is being refuelled.
Mark scheme
friction between the fuel and the pipe can build up charge (1); earthing lets the charge flow safely to the ground, so there is no spark that could ignite the fuel vapour (1)
Model answer
Fuel flowing through the pipe can build up charge. Earthing lets the charge flow safely to the ground, so no spark forms that could ignite the fuel.
A student touches a Van de Graaff generator and her hair stands on end. Explain why.
Mark scheme
charge from the generator spreads onto her hair (1); each hair has the same type of charge (1); like charges repel, so the hairs move apart / stand on end (1)
Model answer
Charge from the generator spreads onto each hair. All of the hairs have the same charge, so they repel each other and stand out.
Explain how a lightning conductor protects a tall building.
Mark scheme
a metal rod / conductor at the top of the building, connected to earth (1); charge flows through the conductor to the ground (1); so the charge does not pass through the building / the building is not damaged (1)
Model answer
The lightning conductor is a metal rod connected to the ground, so when lightning strikes, the charge flows safely to the ground through the rod instead of through the building.
A metal rod held in the hand cannot be charged by rubbing, but a plastic rod can. Explain why.
Mark scheme
metal is a conductor so charge flows away through the hand / body to earth (1); plastic is an insulator so charge stays on it (1)
Model answer
Metal is a conductor, so any charge flows away through the person's body to the Earth. Plastic is an insulator, so the charge stays on it.
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