Static Electricity (T2) Flashcards
Describe static electricity and how it works..
The effect of charge which is stationary.
Occurs when insulating materials are rubbed together.
Friction causes some electrons to be scraped off the surface atoms of a material, leaving that material short of electrons and the other material with a surplus.
The material that has lost electrons has a positive charge and vice versa.
Opposite charges attract.
Give some common examples of static electricity..
- a balloon rubbed on a sweater made of nylon or polyester
- rubbing feet on man made fibre carpets and touching a radiator
- a car on a long journey on a dry summer’s day
What is one of the most spectacular examples of static electricity and how does it come about?
Lightning.
- clouds build up enormous charge due to the friction of the wind or air circulating within, then the charge rushes down to Earth through the air in a lightning bolt
- the discharging currents that flow can be as large 20,000A and it usually takes place in 0.1s
- the air heats up to around 30,000 deg. C
- at these high temperatures the air around the bolt of lightning expands at supersonic speeds
- as the sound waves travel outward they slow down and interact with the air and ground, causing the prolonged claps and rumbles that we associate with thunder
List some uses of static electricity..
- electrostatic spray painting
- inkjet printers
- photocopiers
- electrostatic precipitators
How does electrostatic paint spraying work and why is it used?
It is used to paint awkwardly shaped objects such as bicycle frames, where a normal spray gun can be time consuming and very wasteful
How does electrostatic paint spraying work and why is it used?
It is used to paint awkwardly shaped objects such as bicycle frames, where a normal spray gun can be time consuming and very wasteful.
As the droplets of paint emerge from the spray can, they are charged.
They all carry the same charge therefore repel and spread out, forming a fine spray.
The metal bicycle frame has a wire attached to an electrical supply giving the frame an opposite charge.
The paint droplets are therefore attracted to the surface of the frame, including hard to reach places like corners that may not otherwise have received a good coating.
How do inkjet printers work?
Each spot of ink is given a charge so that it falls between a pair of deflecting plates.
Electrostatic forces direct it to the correct position.
The charges on the plates change hundreds of times each second so that each drop falls in a different position, forming pictures and words as required.
How do photocopiers work with regards to static electricity?
Positive charges are sprayed onto a rotating drum whose surface is coated with a metal called selenium.
A bright light is shone onto the sheet of paper to be copied.
The white parts of the paper reflect light onto the drum, the dark or printed parts do not.
In those places where light is reflected onto the drum, the charge remains.
A fine negatively charged carbon fibre called toner is blown across the drum and sticks to just those parts of the drum that are charged.
A sheet of paper is then pressed against the drum and picks up the pattern of the carbon powder.
The powder is the fixed in place by a heater.
How do electrostatic precipitators work and why are they used?
The smoke from heavy industrial plants carries small particles of ash and dust into the environment, causing health problems and damage to buildings.
Electrostatic precipitators can help remove these pollutants from the smoke.
As the smoke rises up the chimney it passes through a mesh of highly charged wires.
The wires are at a voltage of approx. -50,000V.
As the smoke passes through the mesh, the ash and dust particles become negatively charged.
Higher up the chimney these charged particles are attracted by and stick to large metal earth plates.
The cleaner smoke is then released into the atmosphere.
When the earthed plates are completely covered they are given a sharp rap so the dust and ash falls into collection boxes which are later emptied.
How can static electricity cause issues when refuelling aircraft and / or fuel tankers transporting fuel on roads, and what is the solution?
As aircraft fly through the air they become charged with static electricity.
The same goes for fuel tankers transporting fuel for long distances along roads.
As the charge increases so does the potential difference between the vehicle and the earth.
This creates a risk of charges escaping to earth as a spark during refuelling.
The solution
How can static electricity cause issues when refuelling aircraft and / or fuel tankers transporting fuel on roads, and what is the solution?
As aircraft fly through the air they become charged with static electricity.
The same goes for fuel tankers transporting fuel for long distances along roads.
As the charge increases so does the potential difference between the vehicle and the earth.
This creates a risk of charges escaping to earth as a spark during refuelling.
The solution is to earth the vehicle as soon as it lands or stops, before refuelling commences.
What are two simple ways to investigate static electricity?
- rub some insulating material with a duster then hold it close to tiny scraps of paper or expanded polystyrene spheres to see how much attraction is generated.
- charge up a plastic comb or ruler by rubbing it, then hold it close to the water coming from a tap to give a very slow narrow stream.
Why does static electricity only work with insulators and not conductors?
Electrons find it nearly impossible to travel through insulators or across their surface, so charges built up due to friction tend to stay in one place for long periods of time.
Explain what a Van de Graaf generator is and what it does..
It is an electrostatic generator.
It was invented by American physicist Robert J. Van de Graaf in 1929.
It uses a moving belt to accumulate high amounts of electrical potential on a hollow metal dome on top of a stand.
A motor turns the drive belt and friction between the rubber band and the rollers starts to build up huge amounts of charge.
The charge is deposited on thew metal dome, which is a conductor, but which is insulated from everything else so it can store the charge.
