# KS4 Electricity – Static electricity

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KS4 Electricity – Static electricity

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Charge Particle Charge Proton +1 Neutron none Electron -1

Charge, attraction and repulsion

Attraction and repulsion
repel Positive and positive ________ Negative and negative ________ Positive and negative ________ repel attract Like charges repel, unlike charges attract.

Charging objects What do we call the force you get when two materials rub together? Friction Let’s say you rub an insulator with a cloth, two things can happen: Electrons move from the cloth to the insulator. B. Electrons move from the insulator to the cloth. Let’s look at the two cases in more detail.

Electrons move from the insulator to the cloth
What charge has the cloth? The cloth becomes negatively charged. + + + + What charge has the insulator? The insulator becomes positively charged. It is only the electrons that are free to move.

Electrons move from the cloth to the insulator
What charge has the cloth? The cloth becomes positively charged. What charge has the insulator? The insulator becomes negatively charged. It is only the electrons that are free to move.

Identifying an unknown charge
If you have a rod with an unknown charge you can identify the charge using two methods. If you bring it near a positively charged rod and it is attracted to the rod then the unknown charge must be ________. negative If you bring it near a positively charged rod and it is repelled by the rod then the unknown charge must be _________. OR positive

Identifying an unknown charge
If the rod is a negative rod then…….. If you bring it near a negatively charged rod and it is attracted to the rod then the unknown charge must be ________. positive If you bring it near a negatively charged rod and it is repelled by the rod then the unknown charge must be _________. negative

Inducing a temporary charge
If you bring a negatively charged rod near a piece of paper, why does the paper stick to the rod? The paper has no charge! As the rod approaches the paper, the electrons in the paper are repelled away from the rod. This makes one side of the paper negative and one side positive, a charge has been induced on the paper and the positive side of the paper is attracted to the negative rod.

Inducing a temporary charge
If you bring a positively charged rod near a piece of paper, why does the paper stick to the rod? The paper has no charge! As the rod approaches the paper, the electrons in the paper are attracted towards the rod. This makes one side of the paper negative and one side positive, a charge has been induced on the paper and the negative side of the paper is attracted to the positive rod.

Uses of static electricity
_______________ Spray-painting Printers Photocopiers Pollutant-removers

The electrostatic smoke precipitator
A metal grid at a very high v______ runs down the middle of the chimney. E______ metal plates run down the inside of the chimney. Dirty smoke p______ become charged in the electric field. These charged particles are a______ to the earthed metal plates where they lose their charge and fall back down the chimney. Result – C____ smoke out of top of chimney. oltage arthed articles ttracted lean chimney wall very high voltage on metal grid earthed metal plate dirty smoke

The electrostatic paint spray
The spray gun is designed to produce tiny droplets of paint. The paint spray nozzle is connected to one terminal of an electrostatic generator. The other terminal is connected to the metal panel, which is earthed. As a result the charged droplets are attracted to the car body panel. This gives a uniform coating of paint. Also, the droplets travel along the lines of force of the field to reach hidden parts of the panel.

Electrostatic generator
Spraying a car with paint + + + - + - - - + - - - - - - Paint gun nozzle has a positive charge Car is negatively charged Electrostatic generator The nozzle is connected to one terminal of an electrostatic generator. The other terminal is connected to the metal panel, which is earthed.

Dangers of Charge Fuel filling, paper rollers and grain shoots are all charge problems. As the fuel flows along the pipe or paper rolls over rollers or grain shoots out of tubes, static can build up. This can easily lead to a spark and then an explosion. To prevent this happening, the nozzles or rollers are made out of metal so any charge build up is conducted away. Large petrol tankers always have earthing straps between the tanker and the storage tank to prevent the risk of sparks.

Transferring flammable liquids
What prevents large static charges building up that could cause a possible explosion? nozzle from tanker underground tank or aeroplane tank. electrical link

How is electrolysis used?
Anode is impure copper. This dissolves. Cathode starts as a thin piece of pure copper. MORE copper is deposited C a t h o d e C a t h o d e A n o d e A n o d e Cu2+ Cu2+ Cu2+ Cu2+ Cu2+ Cu2+ Cu2+ Copper sulphate solution electrolyte Cu2+ Cu2+ Sludge (impurities)

Electrolysis During electrolysis how can you increase the mass of material deposited at an electrode? Increase the current Increase the length of time the current flows Increase the resistance Increase the magnetic field Decrease the current x x x

Charge, current and time
We can express a relationship between charge, current and time mathematically using the equation: Charge = Current x time Q=It Charge measured in Coulombs (C) Current measured in Amps (A) Time measured in seconds (s)

  x Q I Formula triangles
Formula triangles help you to rearrange formula, the triangle for Q=It is shown below: Whatever quantity you are trying to find cover it up and it will leave you with the calculation required. …and you are left with the sum… So if you were trying to find current, I….. I = Q t Q …you would cover I up… I t x

A current of 6A flows for 3 minutes. How much charge flows?
Q = It = 6A x (3x60)s = 1080 C Always convert time to seconds!!! In an examination you will not gain a mark for just writing Q=It. You must write out the whole formula: Charge = Current x time

Energy and charge We can express a relationship between charge, energy and potential difference mathematically using the equation: Energy = Charge x Voltage E=QV Charge measured in Coulombs (C) Energy measured in Joules (J) Voltage measured in Volts (V)

  x E Q Formula triangles
Formula triangles help you to rearrange formula, the triangle for E=QV is shown below: Whatever quantity you are trying to find cover it up and it will leave you with the calculation required. …and you are left with the sum… So if you were trying to find charge, Q….. Q = E V E …you would cover Q up… Q V x

Formula triangles This is a flash movie – click on the letter you want to cover to start the animation

A charge of 100 C is delivered at a potential difference of 5V
A charge of 100 C is delivered at a potential difference of 5V. How much energy is delivered? E = QV = 100 C x 5 V = 500 J What is 500J in KJ? 0.5 kJ In an examination you must always give the units. If you do not you will lose a mark.

What is the charge on an electron?
Positive Negative Neutral Depends upon the atom

What force can be used to charge insulators?
Gravity Friction Weight Energy

If a current of 6A is run through a device for 6 seconds
If a current of 6A is run through a device for 6 seconds. What charge is delivered to the device? 1A 36A 1C 36C

If a kettle has a 13A current and is on for 2 minutes, what charge is delivered to the kettle?

If 6C of charge is delivered at a potential difference of 5V, how much energy is delivered?
1.2 J 11 J 30 J 30 kJ