Observing the electric force How electrostatics works Problem electrostatics Positive use of electrostatics

Electrostatics is the science of static, or stationary, electricity. Electrostatics operates in electrical insulators, and this is where it differs from current electricity that needs electrical conductors to facilitate electron flow.

Observing the electric force
You can observe static electricity if you run a plastic comb through your hair, then place the comb near small pieces of paper. The paper is attracted to the comb. This happens because the charged comb induces an opposite charge in the paper and as opposite charges attract, the paper sticks to the comb. Another graphic example is rubbing a balloon against a woolen or synthetic jumper, then putting the balloon against a wall or the ceiling. Attraction of opposite charges holds the balloon in place. Try holding a charged balloon over your hair for another interesting experience! Electrostatics can be a problem, but it has very important applications too.

Charge and induction

How electrostatics works
When a comb is run through your hair charges pass between your hair and the comb, so the comb becomes charged either positively or negatively, and the hair oppositely charged. When the comb is brought close to paper an opposite charge is induced in the paper, and the opposite charges attract. The charges move from one insulator to another on vigorous contact (i.e. by rubbing) to produce the two oppositely charged objects. Then polarisation of charge is induced charges are induced in other insulators close by.

Problem electrostatics
In our modern world of plastics and synthetic fibres static is a problem. Dusting can be frustrating for example if a plastic item is rubbed with a duster. The item becomes charged, and attracts more dust from the air! Anti static cleaners reduce the charges so that is makes dusting more effective. Clothes in the washer rub against each other and get charged. When worn with different fibres they can cling together by attraction. Additives in the rinse can again reduce the charges formed. Technicians assembling computer components have to wear a conducting arm band, connected to an Earth, to prevent the build up of static charges that can be fatal to computer components.

Positive use of electrostatics
Electrostatics is used in everyday life precisely because of its charged properties.

The ubiquitous photocopier is a common example of putting electrostatics to good use. Basically a charged silicon plate, formed as a drum, is charged. Light reflects from an image on the printed page and this produces a variation in charges in the same pattern as the printed page on the drum. A powder (toner) is sprayed over the drum, taking up the pattern stored on the drum. This pattern is then transferred to a sheet of blank paper as the paper is rolled over the drum. The toner is then heated to fuse it to the paper and an exact copy is produced - all by electrostatics. A laser printer works in a similar fashion.

The spray painting of cars is also much more efficient by utilising the electrostatic charges formed as the paint leaves the spray gun. The car frame is charged oppositely to that of the paint droplets. The paint is then attracted to the frame, saving loss at the edges and ensuring that the paint penetrates all the inward folds that might otherwise be missed.

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