5.1 static

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5.1 Static 9 January 2011 Have you ever received a static electric shock? Where? What caused it?

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What do the following pictures have in common?

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Aims

• Show that when insulating objects are rubbed together they become charged

• Explain that there are repulsive forces between objects with similar charge and attractive forces with opposite charges

• State that a flow of charge is a current

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Triboelectric effect (charging by rubbing)

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Charges and electrostatics

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cloth

acetate rod

Rub an acetate rod with a cloth.

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After it has been rubbed, the rod has a positive

charge, and the cloth has a negative charge.

A possible explanation is that some electrons have

been transferred from the cloth to the rod.

both are charged

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polythene rod

polythene rod

rubbed ends repel

The ends of two polythene rods rubbed with a cloth

will repel each other.

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If one polythene rod is replaced with a rubbed acetate

rod, the two ends will attract.

polythene rod

acetate rod

rubbed ends attract

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It can be shocking.

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It can be annoying –

or even dangerous.

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It can be annoying –

or even dangerous.

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It can be annoying –

or even dangerous.

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It can be annoying –

or even dangerous.

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It can be useful.

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It can be useful.

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It can be useful.

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It can be useful.

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Charging by rubbing

• Electrical effects can be produced by rubbing two materials together

• When you rub a piece of plastic it is somehow changed, it can then effect objects at a distance.

• The plastic has been charged

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Two types of charge

• If you rub identical plastic rods and then hold them close together, the rods push apart – they repel

• The forces they exert on each other are very small, so you can only see the effects if one of the rods are free to move

• If you do this with different plastic you find some pairs that attract each other

• The explanation is that there are two kinds of charge, we call this positive and negative

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Where does this charge come from?

• Scientists believe that charge is not made but is moved around when two objects rub

• If you rub a plastic rob with a cloth, both the rod and the cloth become charged

• Each object gets a different charge; rubbing separates charge!