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IGCSE Electricity – Charge

Aims:Describe simple experiments using electrostatic chargesState that there are positive and negative chargesState that unlike charges attract and that like charges repelState that charge is measured in coulombsDescribe charging by induction Recall and use the simple electron model to distinguish between conductors and insulators and give examples.

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Charge

Particle Charge

Proton

Neutron

Electron

+1

none

-1

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Charge, attraction and repulsion

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Attraction and repulsion

Positive and positive ________

Negative and negative ________

Positive and negative ________

repel

repel

attract

Like charges repel, unlike charges attract.

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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:

A. 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.

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Electrons move from the insulator to the cloth

Electrons move from the insulator to the cloth.

The cloth becomes negatively charged.

The insulator becomes positively charged.

It is only the electrons that are free to move.

What charge has the cloth?

What charge has the insulator?

+ ++ +

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Electrons move from the cloth to the insulator

Electrons move from the cloth to the insulator.

The cloth becomes positively charged.

The insulator becomes negatively charged.

What charge has the cloth?

What charge has the insulator?

It is only the electrons that are free to move.

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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)

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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

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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 ________.

If you bring it near a positively charged rod and it is repelled by the rod then the unknown

charge must be _________.

negative

positive OR

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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 ________.

If you bring it near a negatively charged rod and it is repelled by the rod then the unknown

charge must be _________.

positive

negative

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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

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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.

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+ - + - + -

+ - + - + -

+ - + - + -

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.

Inducing a temporary charge

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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.

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To do

• P171&173 Answer all questions

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What is the charge on an electron?

A. Positive

B. Negative

C. Neutral

D. Depends upon the atom

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What force can be used to charge insulators?

A. Gravity

B. Friction

C. Weight

D. Energy

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

A. 1A

B. 36A

C. 1C

D. 36C

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

A. 26 C

B. 6.5 C

C. 1560 C

D. 0.23 C

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If 6C of charge is delivered at a potential difference of 5V, how much energy is delivered?

A. 1.2 J

B. 11 J

C. 30 J

D. 30 kJ

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• 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

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• 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