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KS4 Electricity – Static electricity. Teacher’s Notes. A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000). Notes Page View. Normal View. Flash Files.

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### KS4 Electricity – Static electricity

A slide contains teacher’s notes wherever this icon is displayed -

To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000).

Notes Page View

Normal View

Flash Files

A flash file has been embedded into the PowerPoint slide wherever this icon is displayed –

These files are not editable.

+1

Proton

none

Neutron

-1

Electron

repel

Positive and positive ________

Negative and negative ________

Positive and negative ________

repel

attract

Like charges repel, unlike charges attract.

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.

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

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

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.

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

oltage

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.

arthed

articles

ttracted

lean

chimney wall

very high voltage on metal grid

earthed metal plate

dirty smoke

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 areattracted to the car body panel.

This gives auniform coatingof paint.

Also, the droplets travel along the lines of force of the field to reach hidden parts of the panel.

+

+

+

-

+

-

-

-

+

-

-

-

-

-

-

Paint gun

nozzle has a

positive

charge

Car is negatively charged

Electrostatic generator

The other terminal is connected to the metal panel, which is earthed.

The nozzle is connected to one terminal of an electrostatic generator.

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

Transferring flammable liquids problems.

What prevents large static charges building up that could cause a possible explosion?

nozzle from tanker

underground tank or aeroplane tank.

How is electrolysis used? problems.

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 problems.

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 problems.

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)

Formula triangles problems.

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. problems.How much charge flows?

Always convert time to seconds!!!

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

Energy and charge problems.

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)

Formula triangles problems.

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

A charge of 100 C is delivered at a potential difference of 5V. How much energy is delivered?

What is 500J in KJ?

E = QV

= 100 C x 5 V

= 500 J

0.5 kJ

In an examination you must always give the units.

If you do not you will lose a mark.

Positive 5V.

Negative

Neutral

Depends upon the atom

What is the charge on an electron?

Gravity 5V.

Friction

Weight

Energy

What force can be used to charge insulators?

1A 5V.

36A

1C

36C

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

26 C 5V.

6.5 C

1560 C

0.23 C

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

1.2 J 5V.

11 J

30 J

30 kJ

If 6C of charge is delivered at a potential difference of 5V, how much energy is delivered?