Static electricity

Define — 4 marks

A student is preparing an experiment to investigate the properties of charged objects. She rubs a polythene rod with a cloth and observes that the rod becomes negatively charged. She then brings the charged rod near to some small pieces of paper without touching them, and the paper pieces jump towards the rod.

(a) Define what is meant by static electricity. [1 mark]
(b) Define the term 'electric field' in the context of the charged rod. [1 mark]
(c) The paper pieces are attracted to the negatively charged rod. Define what happens when a neutral object becomes polarised and explain why the paper is attracted to the rod. [2 marks]

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(a) The accumulation/build-up of charge on an object (or in one place) / charge that does not move / stationary charge
(b) The region around a charged object where another charged object experiences a force / where an electric force acts
(c) Polarisation is when the electrons in the paper are repelled away from the negative rod (or positive charges move towards the rod) / the distribution of charge becomes uneven
(c) The positive charges in the paper are now closer to the negative rod than the negative charges / opposite charges attract / the attractive force is stronger than the repulsive force

State — 4 marks

A student rubs a polythene rod with a duster. The rod becomes negatively charged and is then brought near to small pieces of paper on a desk. The paper pieces are attracted to the rod even though they are initially uncharged.

(a) State what happens to electrons in the polythene rod during the rubbing process. [1 mark]
(b) State the type of charge induced on the surface of the paper pieces that face the negatively charged rod. [1 mark]
(c) State two reasons why the paper pieces are attracted to the rod despite being initially uncharged. [2 marks]

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(a) Electrons are transferred from the duster to the polythene rod / electrons move onto the polythene rod (1 mark)
(b) Positive charge is induced on the surface of the paper facing the rod (1 mark)
(c) The negatively charged rod repels electrons in the paper, leaving a positive charge on the near surface (1 mark)
(c) Opposite charges attract, so the positive charge on the paper is attracted to the negative charge on the rod (1 mark)

Explain — 2 marks

A student rubs a balloon on their hair and then holds it near some small pieces of paper. The pieces of paper are attracted to the balloon and stick to it.

(a) Explain why the balloon becomes negatively charged when rubbed on hair. [1 mark]
(b) Explain why the pieces of paper are attracted to the negatively charged balloon. [1 mark]

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(a) Electrons are transferred from the hair to the balloon / rubbing causes electrons to move to the balloon
(b) The negatively charged balloon induces a positive charge on the near surface of the paper / the paper becomes polarised / electrons in the paper are repelled away from the balloon, leaving positive charge closer to the balloon

Describe — 2 marks

A student rubs a polythene rod with a cloth. The rod becomes negatively charged and can attract small pieces of paper. The student then touches the charged rod with their finger and notices the paper pieces fall away.

(a) Describe what happens to the electrons when the polythene rod is rubbed with the cloth. [1 mark]
(b) Describe why the pieces of paper no longer stick to the rod after the student touches it with their finger. [1 mark]

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(a) Electrons are transferred from the cloth to the polythene rod / electrons move from the cloth to the rod
(b) The charge leaks away through the student's body to the ground / electrons are discharged through the finger / the rod becomes electrically neutral so it no longer attracts the paper

Calculate — 2 marks

A student rubs a polythene rod with a cloth. The rod becomes negatively charged and attracts small pieces of paper. The student then uses the charged rod to pick up 8 pieces of paper in 4 seconds.

Calculate the rate at which the student picks up pieces of paper in pieces per second. [2 marks]

Show mark scheme

{'mark': 1, 'description': 'Correct substitution into formula: rate = 8 ÷ 4 or equivalent working shown'}
{'mark': 1, 'description': 'Correct final answer: 2 pieces per second (or 2 pieces/s)'}

Define — 4 marks

State — 4 marks

Explain — 2 marks

Describe — 2 marks

Calculate — 2 marks

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