GCSE Physics: Static Electricity

A plastic rod carried no overall charge. It has equal number of positive and negative charges. Instead of forming areas of positive charges, and areas of negative charges, the spread out as like charges repel. If a positively charged object is held near to the rod the positive object needs to neutralise itself, ans so take some of the negative charges from the rod. This leaves the rod with positive charge, which the object that was origionally positive now repels.

How a Photocopier works

1. A photoconductive surface is given a positive electrical charge (+).
2. The image of a document is exposed on the surface. This causes the charge to drain away from the surface in all but the image area, which remains uneposed and charged.
3. Negatively charged powder is cascaded over the surface. It electrostatically adheres to the positively charged image area making a visible image.
4. A piece of plain paper is placed over the surface and given a positive charge.
5. The negatively charged powder image on the surface is eletrostatically attracted to the positively charged paper.
6. The powder image is fused to the paper by heat. After the photoconductive surface is cleaned the process can be repeated.

How an Electrostatic Precipitator works

An electrostatic precipitator is an electrical decide for removing impurities such as dust, fumes, or mist from air or other gases. It is used in places where fumes full of impurities are made, such as powerstations powered by fossil fuels. The electrostatic precipitator was developed in about 1906. For filtering particles, the electrostatic precipitator is one of the more expensive options, it is much more efficient and considerably more effective at removing small particles however than alternatives such as air filters.

1. The gas to be purified moves through passages that have charged electrodes suspended in the middle of them. The electrodes are supplied with direct curent at high voltages ranging from 30,000 to 75,000 volts.
2. Beyond the charged electrodes are large metal collector electrodes that are charged, The current applied to the smoke particles gives them a charge the opposite of that of the collector electrodes. The two attract, and so even the smallest particles can be filtered this way.

Periodically the filter must be washed or scraped clean to remove the deposited smoke particles. Electrostatic precipitators are used in eliminating atmospheric pollution from the exhausts of industrial devices such as steam boilers and cement kilns as well as powerstations.

Dangers of Static Electricity and Aircraft

When an aircraft is in flight, rain drops and ice crysstals in teh upper atmosphere can charge the aircraft. The charging of the aircraft is called "precipitation charging." The jet engines, because of the burning gases, can salso charge the aircraft. On military aircraft, the afterburners charge the aircraft very quickly when they are turned on. Fortunately the people inside the aircraft do not get charge. The charge is all on the outside of the aircraft. The charge on the outside of the aircraft is clearly a danger and so decides known as dischargers are fitten to the wings and tail of the aircraft.

A discharger consists of a high resistance resistor that is electrically connected to the metal surface of the aircraft. The end of the resistor has two sharp needle points. The needle points are perpendicular to the resistor and facing in opposite directions. A discharger has a lot of thin metal strips that are connected to the ground. Self-dischargers are used to discharge paper during the printing process. Thin metal strips are used to discharge the paper that comes out of a computer printer or other high speed paper printer or manufacturing machine. Seld-dischargers start to operate when the electric field becomes high. A high electric field causes a corona discharge from the needle point. The needle points are very sharp and therefore a plastic guard is placed around the point to keep people from being injured. Each needle point can have a current up to about 4 microamps when the voltage is high. The discharge stops when the voltage drops, probably about at the 3,000 volt level. The dischargers on the aircraft work in much the same way, in that most aircraft have conductive rubber tyres, therefore when the aircraft lands, any charge on the aircraft is discharged to the ground when the wheels touch. No charge can get inside the plane, and poses no risk to passengers.