1. P2 Static Electricity Revision Mock 2015

2. Electrons move from the cloth to the insulator.
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.

3. 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.

5. 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.

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

7. 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

8. How does static charge reduce pollution?
A precipitator in the chimney of a power station uses static electricity to filter smoke particles from waste gases.
The smoke particles pass through a charged grid and pick up a negative charge.
positively- charged metal plates
They are then attracted
to the positively-charged collecting plates.
smoke particles
The smoke particles lose their charge and fall back down the chimney, so the waste gases emitted are free of polluting smoke.
metal grid at a high voltage

9. 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.

10. 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.

11. 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.

12. 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

13. Definition of electric current
Electric current is the RATE of flow of charge
What does mean?
This means the amount of charge passing a point in 1 second in a circuit is the electric current.
Remember
electrons are
negatively charged

14. Mathematical definition of electric current
Note for higher paper you are expected to be able rearrange this equation