5.1 static

5.1 Static9 January 2011

Have you ever received a static electric shock?

Where? What caused it?

What do the following pictures have in common?

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

Triboelectric effect (charging by rubbing)

Charges and electrostatics

cloth

acetate rod

Rub an acetate rod with a cloth.

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

polythene rod

polythene rod

rubbed ends repel

The ends of two polythene rods rubbed with a cloth

will repel each other.

If one polythene rod is replaced with a rubbed acetate

rod, the two ends will attract.

polythene rod

acetate rod

rubbed ends attract

It can be shocking.

It can be annoying –

or even dangerous.

It can be annoying –

or even dangerous.

It can be annoying –

or even dangerous.

It can be annoying –

or even dangerous.

It can be useful.

It can be useful.

It can be useful.

It can be useful.

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

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

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!