2.25 explain some uses of electrostatic charges, e.g in photocopiers and inkjet printers

Photocopiers

In photocopiers, there is an image plate which is positively charged, an image of what you are photocopying is then projected onto it. The charge leaks away from the white/light parts of what your copying as they make light fall on the plate. The dark/black parts of what your copying remain charged and attract negatively charged black power, which is transferred onto positively charged paper. Next, the paper is heated to stick the powder down.

Inkjet printers

In an inkjet printer, tiny droplets of ink are forced out of a fine nozzle, this makes them electrically charged. The droplets are then deflected as they pass between two metal plates. A voltage is applied to the plates, one is negative and the other is positive. The droplets are attracted the the plate of the opposite charge and repelled from the plate with the same charge - the size and direction of the voltage across each plate constantly changes so that each droplet is deflected to hit a different place on the paper.

2.23 explain electrostatic phenomena in terms of the movement of electrons

This is quite confusing and may need a few reads to fully understand...

The movement of electrons is responsible for all phenomena relating to current electricity. However, electrostatic phenomenon, such as electrostatic induction , is the transfer of electrons from one body to another.

For example, polythene and cloth. When they are rubbed together, the rod will gain electrons and become positively charged and the cloth will lose electrons and become negatively charged.

2.24 explain the potential dangers of electrostatic charges, e.g when fuelling aircraft and tankers

Problem

As fuel flows out of a filler pipe (the pipe thing that you put in your car, etc), static electricity can build up. This can easily lead to a spark, which can cause a fire in dusty/fumy places.


Solution

Make the nozzle of the filler pipe out of metal so that the charge is conducted away instead of building up (as the building up of electrostatic charge will cause a spark).

It is also good to have earthing straps between a feeling tank and the fuel pipe, to earth the charge, avoiding a build up of the charge.

2.22 understand that there are forces of attraction between unlike charges and forces of repulsion between like charged

- Two materials with opposite electrostatic charges are attracted to each other
- Two materials with the same electrostatic charge will repel

NOTE: like magnets, these forces get weaker the further apart the two materials are

2.21 explain that positive and negative electrostatic charged are produced on materials by the loss and gain of electrons

When two insulating materials are rubbed together, they become electrostatic ally charged. This is because the electrons are transferred from one material onto the other. For example, when polythene rod (this has a negative charge) is rubbed against a cloth, (this has a positive charge), all the electrons move from the cloth to the polythene rod. This leaves the polythene rod negatively charged (as it has gained electrons) and the cloth positively charges (as it has lost electrons).

A way of remembering this is with the anagram, NIGPIL (yes i made it up, if you remember it tough, it does work!). It stands for...
Negative Is Gain - as the material that gains electrons becomes negatively charged
Positive Is Loss - as the material that loses electrons becomes posotively charged

NOTE: Which material transfers which electrons will depend on the two materials involved - it will not always be the cloth losing electrons/the rod gaining electrons.

2.20 describe experiments to investigate how insulating materials can be charged by friction

When two insulating materials are rubbed together, electrons will pass from one insulator onto the other insulator.

Rub a cloth on a polythene rod. Electrons will move from the duster to the rod. The rod will become negatively charged and the cloth will become equal positively charged. To check, hold the rod and the cloth near a pile of small bits of paper,  the bits of paper will be attracted to the rod/cloth as they are electrically charged.

Alternatively, you could use an acetate rod and cloth, it involves the same process and, therefore, the same outcome will occur. The only difference is that the acetate rod will be positively charged and the cloth will become negatively charged.

2.19 identify common materials which are electrical conductors or insulators, including metals and plastics

Materials that are electrical conductors conduct charge easily (basically, a current can flow through them), they are usually metals (although not always). Examples include copper and silver

Electrical insulators do not conduct charge well at all (basically, a current can't flow). Examples include plastic and rubber.