© boardworks ltd 2003 ks4 electricity – static electricity
TRANSCRIPT
© Boardworks Ltd 2003
KS4 Electricity – Static electricity
© Boardworks Ltd 2003
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Charge
Particle Charge
Proton
Neutron
Electron
+1
none
-1
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Charge, attraction and repulsion
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Attraction and repulsion
Positive and positive ________
Negative and negative ________
Positive and negative ________
repel
repel
attract
Like charges repel, unlike charges attract.
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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:
A. 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.
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Electrons move from the insulator to the cloth
Electrons move from the insulator to the cloth.
The cloth becomes negatively charged.
The insulator becomes positively charged.
It is only the electrons that are free to move.
What charge has the cloth?
What charge has the insulator?
+ ++ +
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Electrons move from the cloth to the insulator
Electrons move from the cloth to the insulator.
The cloth becomes positively charged.
The insulator becomes negatively charged.
What charge has the cloth?
What charge has the insulator?
It is only the electrons that are free to move.
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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 ________.
If you bring it near a positively charged rod and it is repelled by the rod then the unknown
charge must be _________.
negative
positive OR
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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 ________.
If you bring it near a negatively charged rod and it is repelled by the rod then the unknown
charge must be _________.
positive
negative
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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.
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+ - + - + -
+ - + - + -
+ - + - + -
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.
Inducing a temporary charge
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Uses of static electricity
Uses of static electricity:
1. _______________
2. _______________
3. _______________
4. _______________
Spray-painting
Printers
Photocopiers
Pollutant-removers
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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.
chimney wall
earthed metal plate
very high voltage on metal grid
dirty smoke
oltagearthed
articlesttracted
lean
The electrostatic smoke precipitator
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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.
The electrostatic paint spray
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+++
+ --
-
--
-
--
-
-
Paint gunnozzle has apositive charge
Car is negatively charged
+
Spraying a car with paint
The nozzle is connected to one terminal of an electrostatic generator.
The other terminal is connected to the metal panel, which is earthed.
Electrostatic generator
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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.
Dangers of Charge
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underground tank or aeroplane tank.
nozzle from tanker
electrical link
Transferring flammable liquids
What prevents large static charges building up that could cause a possible explosion?
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How is electrolysis used?
Cu2+
Cu2+Cu2+
Anode is impurecopper. This dissolves.
Cathodestartsas a thinpieceof purecopper. MOREcopper isdeposited
Sludge (impurities)
Copper sulphate solutionelectrolyte
Anode
Cathode
Cu2+Cu2+Cu2+Cu2+Cu2+Cu2+
Cathode
Anode
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Electrolysis
Increase the current
Increase the length of time the current flows
Increase the resistance
Increase the magnetic field
Decrease the current
x
xx
During electrolysis how can you increase the mass of material deposited at an electrode?
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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)
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Formula triangles
Q
I t
x
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.
So if you were trying to find current, I…..
…you would cover I up…
…and you are left with the sum…
I = Q
t
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A current of 6A flows for 3 minutes. How much charge flows?
Q = It
= 6A x (3x60)s
= 1080 C
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
Always convert time to
seconds!!!
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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)
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Formula triangles
E
Q V
x
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.
So if you were trying to find charge, Q…..
…you would cover Q up…
…and you are left with the sum…
Q = E
V
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Formula triangles
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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
In an examination you must always give the units.
If you do not you will lose a mark.
What is 500J in KJ?
0.5 kJ
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What is the charge on an electron?
A. Positive
B. Negative
C. Neutral
D. Depends upon the atom
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What force can be used to charge insulators?
A. Gravity
B. Friction
C. Weight
D. Energy
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If a current of 6A is run through a device for 6 seconds. What charge is delivered to the device?
A. 1A
B. 36A
C. 1C
D. 36C
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If a kettle has a 13A current and is on for 2 minutes, what charge is delivered to the kettle?
A. 26 C
B. 6.5 C
C. 1560 C
D. 0.23 C
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If 6C of charge is delivered at a potential difference of 5V, how much energy is delivered?
A. 1.2 J
B. 11 J
C. 30 J
D. 30 kJ