# IGCSE Electricity – Charge

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IGCSE Electricity – Charge
Aims: Describe simple experiments using electrostatic charges State that there are positive and negative charges State that unlike charges attract and that like charges repel State that charge is measured in coulombs Describe charging by induction Recall and use the simple electron model to distinguish between conductors and insulators and give examples.

Charge Particle Charge Proton +1 Neutron none Electron -1

Charge, attraction and repulsion

Attraction and repulsion
repel Positive and positive ________ Negative and negative ________ Positive and negative ________ repel attract Like charges repel, unlike charges attract.

Charging objects What do we call the force you get when two materials rub together? Friction Let’s say you rub an insulator with a cloth, two things can happen: Electrons move from the cloth to the insulator. B. Electrons move from the insulator to the cloth. Let’s look at the two cases in more detail.

Electrons move from the insulator to the cloth
What charge has the cloth? The cloth becomes negatively charged. + + + + What charge has the insulator? The insulator becomes positively charged. It is only the electrons that are free to move.

Electrons move from the cloth to the insulator
What charge has the cloth? The cloth becomes positively charged. What charge has the insulator? The insulator becomes negatively charged. It is only the electrons that are free to move.

Experiment 1 Charge up one of the plastic strips
Check the charge using the charge measuring device and the data logger Was the charge positive or negative Can you explain what has happened (use the word electrons)

Experiment 2 Charge up the same rod as in experiment 1 and attach it to the cradle Now charge up another rod and bring it close to the first What happens? What charge is on the new rod? Check with the charge measuring device

Identifying an unknown charge
If you have a rod with an unknown charge you can identify the charge using two methods. If you bring it near a positively charged rod and it is attracted to the rod then the unknown charge must be ________. negative If you bring it near a positively charged rod and it is repelled by the rod then the unknown charge must be _________. OR positive

Identifying an unknown charge
If the rod is a negative rod then…….. If you bring it near a negatively charged rod and it is attracted to the rod then the unknown charge must be ________. positive If you bring it near a negatively charged rod and it is repelled by the rod then the unknown charge must be _________. negative

Experiment 3 Charge up a rod and bring it near to some small pieces of paper Try holding your rod near a stream of water from a tap Rub a balloon on your sweater (or hair) place it gently against the wall Can you explain what happens

Inducing a temporary charge
If you bring a negatively charged rod near a piece of paper, why does the paper stick to the rod? The paper has no charge! As the rod approaches the paper, the electrons in the paper are repelled away from the rod. This makes one side of the paper negative and one side positive, a charge has been induced on the paper and the positive side of the paper is attracted to the negative rod.

Inducing a temporary charge
If you bring a positively charged rod near a piece of paper, why does the paper stick to the rod? The paper has no charge! As the rod approaches the paper, the electrons in the paper are attracted towards the rod. This makes one side of the paper negative and one side positive, a charge has been induced on the paper and the negative side of the paper is attracted to the positive rod.

Conductors and Insulators
In all of the examples which particles move? Protons do not move in materials (they are trapped away in the nucleus) A good conductor has lots of electrons that are free to move – Free electrons An insulator does not have free electrons.

To do P171&173 Answer all questions

What is the charge on an electron?
Positive Negative Neutral Depends upon the atom

What force can be used to charge insulators?
Gravity Friction Weight Energy

If a current of 6A is run through a device for 6 seconds
If a current of 6A is run through a device for 6 seconds. What charge is delivered to the device? 1A 36A 1C 36C

If a kettle has a 13A current and is on for 2 minutes, what charge is delivered to the kettle?

If 6C of charge is delivered at a potential difference of 5V, how much energy is delivered?
1.2 J 11 J 30 J 30 kJ

Core Describe simple experiments to show the production and detection of electrostatic charges State that there are positive and negative charges State that unlike charges attract and that like charges repel Distinguish between electrical conductors and insulators and give typical examples

Supplement State that charge is measured in coulombs Give an account of charging by induction Recall and use the simple electron model to distinguish between conductors and insulators