Triple Electricity: Static Electricity + something about charge Flashcards

1
Q

What is electric charge?

A

Electric charge is given energy by the battery/power supply, and as it flows around a circuit it converts the energy into other forms in components such as light bulbs, motors etc. Charge can be thought of as an ‘energy carrier’

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2
Q

What is voltage?

A

The number of joules of energy transferred - given to the charge in the case of a battery/power supply; given up by the charge in the case of resistors, etc - as one coulomb of charge passes through a component is equal to the voltage, or potential difference, across it

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3
Q

What is 1 volt equal to?

A

1V = 1J/C

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4
Q

What is the equation between voltage, energy and charge

A

voltage = energy / charge

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5
Q

What is electric current?

A

The flow of charge

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6
Q

What happens when two insulating materials are charged by friction?

A

When two insulating materials (e.g. a polythene rod and a cotton cloth) are rubbed together, they both obtain an electrostatic charge. What has happened is that the electrons have been transferred from the cloth to the rod (outer electrons are easy to remove). This leaves the rod negatively charged (i.e. with more electrons than it should have) and the cloth positively charged (i.e. with fewer electrons than it should have

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7
Q

Why does the electrostatic effect not work on conducting materials?

A

Because any charges that are produced are quickly conducted away

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8
Q

What is an important thing to note about the protons?

A

It is always the electrons that move about - the protons are locked deep down inside the nucleus and cannot jump about or be transferred

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9
Q

Give examples of substances that become positively charged when rubbed

A

Cellulose acetate, glass, wool silk, cotton cloth

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10
Q

Give examples of substances that become negatively charged when rubbed

A

Amber, rubber (e.g. balloons), polythene

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11
Q

What is the triboelectric series?

A

Something that ranks the tendency of materials to gain or lose electrons from the electrostatic effect

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12
Q

What are the forces between like charges and unlike charges?

A

Like charges repel

Unlike charges attract

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13
Q

Explain what happens when an uncharged conducting object (e.g. a metal sphere hanging from an insulating wire) touches a charged insulating material (e.g. a negatively charged polythene rod)

A

If the rod touches the metal sphere, some of the electrons on the rod will move onto the sphere making it negatively charged too.
(The same thing happens if the sphere is connected to the negative terminal of an extra high tension (EHT) power supply i.e. one that can produce potential differences of several thousand volts - or to the negatively charged dome of the Van de Graaff generator)

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14
Q

Explain what happens when a charged insulating material (e.g. a negatively charged polythene rod) is held close to an uncharged conducting object (e.g. a metal sphere hanging from an insulating wire)

A

If the rod is held close to the metal sphere, electrons on it are repelled to the far side, leaving the side closest to the rod positively charged. The sphere is now said to have (temporary) induced charges
However if the sphere is now earthed (e.g. by touching it), electrons in the sphere will take the opportunity to get even further away from the rod by flowing down into the Earth. If the connection is then removed, the sphere will be left with a permanent positive charge - as the electrons will not be able to return to it.
This process is called charging by induction.
* The charged produced is opposite to that on the object that does the inducing (the rod)

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15
Q

Explain how uncharged small particles (e.g. pieces of paper) can be attracted to a charged rod

A

When you rub together the two insulators, electrons are transferred so there are extra electrons on the rod, meaning it has a negative charge
When the small, neutral particle is near the rod, some electrons move away from the rod to the other side of the particle because of the high amount of electrons on the rod
This leaves more protons on on the side of the particle near the rod so there is a positive charge on that side. This creates a force of attraction between the negative charge on the rod and the positive charge on the particle

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16
Q

Explain the main danger of static electricity

A

If the potential difference across a metre of air exceeds about 3 million volts, the air will cease to be an electrical insulator and a spark will pass - the large electric field created by the high voltage will accelerate any ions or electrons that are around to energies where they can create more ions through collisions with neutral molecules - a spark can be though of as an ‘ion avalanche’
There is always a danger that sparking caused by the high potential difference associated with charges could cause a fire or explosion if there are flammable materials around.

17
Q

Explain some examples of dangers of static electricity

A

1) in an aircraft - fuel (an insulator) can pick up an electrostatic charge as it flows through a pipe that could be very dangerous during refuelling operations; so the pipe must be earthed in order to prevent a charge from building up
2) our clothing can become charged with static electricity - when we remove our clothes there is the possibility of receiving a small electric shock as the charges escape to earth
3) In operating theatres it is important that the doctors do not become statically charged when walking around. This is because some of the anaesthetic gases used are explosive - antistatic material is used for the floor surface so that any charge is conducted to the Earth

18
Q

What are some uses of static electricity?

A

Photocopiers and inkjet printers
Electrostatic Precipitation
Electrostatic paint spraying

19
Q

How does an inkjet printer work?

A

Many modern printers use inkjets to direct a fine jet of ink drops onto paper
Each spot of ink is given a charge so that as 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 on paper as required.

20
Q

How does a photocopier work?

A

A rotating drum is coated with a layer of photoconductive material and then given a positive charge
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 the places where the light is reflected onto the drum, the drum loses its charge but where no light is reflected onto the drum the charge remains
Black toner powder that is negatively charged is then blown across the drum and sticks to the remaining charged areas
The drum transfers the toner to a piece of paper and then it is fused to the paper by heat

21
Q

What is electrostatic precipitation?

A

This is done to remove small particles of ash and dust from smoke that is produced at many heavy industrial plants such as steel-making furnaces - the ash and dust can cause health problems and damage to buildings

22
Q

How does electrostatic precipitation work?

A

As the smoke initially rises up the chimney it passes through a mesh of wires that are highly charged (at an approx. voltage of -50,000V)
As they pass 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 earthed plates
The cleaner smoke is then released into the atmosphere
When the earthed plates are completely covered with dust and ash, they are given a sharp rap - the dust and ash fall into collection boxes, which are later emptied

23
Q

How does electrostatic spray painting work?

A

The spray nozzle is connected to the positive terminal of an electrostatic generator
As the paint droplets leave they repel each other and spread out the form a fine cloud of paint
The metal panel to be painted is connected to the negative terminal (or just earthed)
The positively charged paint droplets are therefore attracted to the negatively charged metal panel

24
Q

What are the benefits of electrostatic spray painting?

A

Electrostatic spray painting makes the process of painting much more efficient and less wasteful of paint - also allows paint to be attracted to places, such as tight corners, that might otherwise not receive such a good coating

25
Q

How does lightning occur?

A

Static electricity can build up in the clouds. The current discharges to the earth across the cloud. The air conducts the electricity.This causes lightning - a flow of charge through the atmosphere