- Created by: S_webb
- Created on: 12-10-16 19:48
P2.1 -- Static electricity:
- Static electricity is caused by an electrostatic charge building up on insulating materials.
- If one rubs two insulating materials against each other, electrons may be transferred from one to the other. Objects charged in this way can attract or repel each other; opposite charges attract, like charges repel.
- If you place a balloon with a negative charge against a wall, it will stick to the wall as the electrons in the wall will be repelled and move away, leaving a positive charge (called an induced charge) which attracts the negative charge on the balloon.
P2.2 -- Uses and dangers of static electricity:
- One can pick up electrons just by walking across a carpet or even sitting on a chair; when you then touch a metal object, you feel a small shock as the electrons flow between you and the object. Electrons move through you to earth through the object, or the other way around; this process is called earthing and you are said to be discharged.
- Static electricity can build up on clouds, where it causes a huge spark to form between the cloud and the ground. When the charge particles that make up static electricity move from the cloud to the ground, this results in what we call lightning.
- Electricity can build up as fuel flows through a pipe; this is dangerous as this buildup of static electricity can cause a spark, which would set light to the extremely flammable fuel. In order to prevent this from happening, the aircraft is connected to earth with bonding lines before it is refuelled; this prevents the said buildup from occuring and thus prevents a spark. A similar problem can occur when tankers deliever fuel; in this case, the pipes taking the fuel to underground fuel tanks are made of conducting materials, so again no buildup of charge occurs.
- Static electricity can also be useful, for example in electromagnetic spray painting: the object to be painted is given a negative charge, the spray nozzle is connected to the positive terminal of an electricity supply, the positive paint droplets repel each other and spread out and finally the positive paint droplets are attracted to the negative charges on the surface of the object.
P2.3 -- Electric currents:
- All materials contain electrons. In metals, some of the electrons from each atom are free to move about. When electrons in metals flow, what we call an electric current occurs.
- When a metal wire is placed in an electric circuit, the free electrons, which normally move around randomly in all directions, are pushed around the circuit in one direction by the cell. Cells and batteries supply direct current (moves in only one direction); generators supply alternate current (switches direction).
- The current is the rate of flow of charged particles; the charge (Q, coulombs) is equal to the current (I, amperes) times the time (t, seconds).
P2.4 -- Current and voltage:
- Current is measured by ammeters in series, potential difference by voltmeters in…