Static Electricity

Static electricity is produced when two insulating materials are rubbed together. The friction created by the rubbing, rubs electrons off from one material and onto another material. The charge builds up and the object is statically charged. Charged objects can attract small uncharged objects e.g. small pieces of paper

The one that loses electrons becomes positively charged.

The one that gains electrons becomes negatively charged.

Static electricity occurs in insulators as in conductors charge isn't able to build up as it passes through and straight to the earth, whereas in insulators there are no free electrons to carry the charge away and so the charge builds up inside the insulator.

Basics

- Like charges repel

- Opposite charges attract

In conductors there are free electrons. If friction causes an electron to be rubbed off another electron would easily take its place so no charge is able to build up as each electron removed is replaced. However in insulators there are no free electrons so if friction causes an electron to be rubbed off then it builds up a positive charge and vice versa.

(Don't really need to know this, but it helps)

Charged conductors can be discharged (lose their charge) to the earth by connecting it with a metal strap to the earth. If the object is negatively charged then electrons will travel down the strap and to the earth. If the object is positively charged the electrons will flow from the earth up the strap and to the objects.

If however there is a large potential difference a spark can jump across the gap between the charged object and conductor -which can be dangerous to e.g. petrol stations.

Using an electroscope - If a negatively charged rod is placed over an electroscope then the negative charges attract the positive charges on the metal leaving the negative charges. The negative and negative charges repel each other and so the gold leaf rises.

Water - Water is deflected when a negative or positve charged object is near it as e.g. the negative charges on the rod repel the negative charges in the water and like charges repel the water is deflected.

Charged objects attract small uncharged objects - If a negatively charged rod is placed over uncharged bits of paper it will attract as the negative charges repel the negative charges on the paper, leaving the positive charges 'exposed' and so the positive charges from the paper and negative charges on the rod attract.

Lightning is a form of static electricity. Inside rain clouds ice and water particles are bumping into each other knocking off electrons and becoming charged. As this charge builds up the potential differenc becomes larger. The charge wants to discharge to the earth and as there is a large potential difference a spark is formed which jumps across the gap between the charged cloud and earth to discharge.

Industrial chimneys release smoke which is unreacted carbon particles into the atmosphere which is bad for people with breathing difficulties. An electrostatic percipiator is used to stop smoke particles from leaving chimneys. As smoke rises up the chimney it pass a negatively charged grid and picks up a negative charge. The chimney is lined with positive charged collecting plates which attract the smoke particles to them whilst the rest of the gasses leave the chimney. The collecting plates are earthed and so as soon as the smoke is attracted to the collecting plate it loses its charge and so if the plate is tapped the smoke particles will fall. The collecting plates have to be collected and emptied.

Inside a photocopier is a positively charged drum, a layer of a material which conducts electricty when light shines on it covers the drum. Light shines on the image on the drum causing the charges on the light parts of image to leak away leaving the dark parts with a positive charge. Negatively charged toner powder is spread over the drum. The negative charges of toner attract the positive charges of the image and stick to the dark bits. This is then transferred onto paper and put through rollers under heat and pressure to ensure that the toner sticks.

As paint leaves the nozzel of the spray it picks up a positive charge. The car body is given a negative charge. The positive charged paint droplets attract the negative car body and the paint stays on. This is a much cleaner process as the charges attract to each other nowhere else and so there is less spillage. Also this covers a wider surface area as when the paint leaves the nozzel each droplet of paint picks up a positive charge. The positive charges want to repel each other, as like charges repel, and so want to get as far away from each other as possible covering a larger area evenly.

When petrol is puumped from a road tanker into a storage tanker it travels through a pipe. The friction between the petrol and pipe can cause a static charge to build up. If this static charge builds up large enough it can cause a spark and egnite the fuel causing an explosion. This can be avoided by earthing the pipe as then charge would not be able to build up as it would be discharged straight to the earth.

Note

-Friction can also be caused by tyres and road

- Petrol is unloaded underground so it is already earthed

The friction between flour and pipe can cause static charge to build up and cause a spark. In dry conditions this could cause and explosion and so in this case the pipe must be earthed to prevent charge from being able to build up, preventing a spark and an explosion.

Hope this helped ***