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GCSE Questions: Static Electricity

Q2.

(a)     The diagram shows a polythene rod being rubbed with a woollen cloth.

The polythene rod becomes negatively charged. Explain how this happens.

[2 marks]

Electrons transfer from the rod to the cloth.

You should always make it clear that you know it is the electrons that are moving from one item to another. As electrons are negative, the item that becomes negative will have gained electrons.

 

(b)     A student put the charged polythene rod onto a balance.

 

 

The rod was separated from the metal pan of the balance by a thin block of insulating material.

The student then held a second charged polythene rod above, but not touching, the first rod. The reading on the balance increased.

 

 

(i)      Explain why the reading on the balance increases.

The rods both have the same charge therefore they repel each other. The force of repulsion creates a downward force on the balance pan and therefore the balance registers a higher reading.

(2 marks)

(ii)     The student observed that the nearer the two rods are to each other, the bigger the increase in the balance reading. What should the student conclude from this observation?

The force of repulsion increases as the distance between the charges decreases

It has to be clear in your answer that you know the repulsive force is due to the interaction of the charges. If you just said 'force increases as distance decreases' you would only get one of the marks.

(2 marks)

 

[Total 6 marks]