Also see: Charge and Electric Current

When certain different insulating materials are rubbed against each other they become electrically charged by friction. The charges stay still on the object.. therefore it is called static electricity. This only happens with insulators, with conductors the charge moves through them and doesn't stay put!

Click here for an interactive program that allows you to see buildup and discharge of static charge.

Electrically charged objects attract small, light objects placed near to them. Heavier objects don't seem to be attracted!

Why is this?

If the electric force due to the attraction is bigger that the weight of the small object then this will make them move. They will jump up and stick to the charged object. This is why statically charged objects get so dusty!

When two electrically charged objects are brought close together, they exert a force on each other. Two charged objects may either pull towards each other (attract) or push each other away (repel). These observations can be explained in terms of two types of charge called positive (+) and negative (-). Two objects which have the same type of charge repel. Two objects which have different types of charge attract.

Like charges repel... opposites attract!

The Van de Graaff Generator makes hair strands all gain the same charge they therefore repel each other. They do so with a force that is greater than the weight of the strands of hair, therefore the strands stand up on end !!

See the animation of lightning

When two different materials are rubbed against each other, electrons, which have a negative charge, are rubbed off one material on to the other. The material which gains electrons becomes negatively charged; the material which loses electrons is left with an equal positive charge.

Charging by Induction

When a charged object is brought near to a neutral one the electric field produced by the charged object disturbs the electron clouds around the atoms in the neutral object, distorting them and causing a disturbance in the balance of charge in the neutral object.

Look at thephoto on the right. The balloons have been 'charged by friction' - rubbed on a woollen claoth and thereby gained electrons. The charged balloons then repelled the electrons near the surface of the man's head giving his head surface a partial positive charge. The negative balloons therefore 'stick' to his head.

If a negatively charged rod is brought near to a neutral piece of paper the electrons on the surface of the paper retreat giving the surface a partial positive charge. This makes the paper attractive to the rod and it jumps up and sticks to it (providing it is not too heavy - because its weight will pull it down).

If a positively charged rod is brought near to a neutral piece of paper the electrons near the surface of the paper advance toward the rod giving the surface a partial negative charge. This makes the paper attractive to the rod and it jumps up and sticks to it (providing it is not too heavy - because its weight will pull it down).

Remember - the protons don't move! They are locked inside the nucleus... only fliuds could have positive nuclei influenced to move because of electric charge!

You should be able, when provided with appropriate information about a situation in which static electricity is dangerous, to explain why it is dangerous and how precautions can be taken to ensure that the electrostatic charge is discharged safely.

Bending Water Jet - Do do this at Home!

Water molecules are 'polar'. That means they have an uneven charge distribution on them. The oxygen atom has a little negative charge and the hydrogens have a little positive charge. If a charged object (like a comb) is brought near to the water the water molecules relign themselves within the stream so that the end of the molecule that has an opposite charge is facing the charged object. opposite charges attract so the molecules pull towards the charged object and you see the stream ned as in the video - try it at home!

The Gold Leaf Electroscope - a detector for static charge

This can be used to detect charged objects. The charged object induces a charge in the two sheets of gold leaf - gold leaf is so light that the electrostatic force of repulsion is much stronger than the weight and the sheets move apart - the greater the charge, the stronger the force and the further apart they move!

Try this useful learning tool to help you learn this topic and/or test your knowledge...