Download - © Boardworks Ltd 2003 KS4 Electricity – Static electricity

© Boardworks Ltd 2003

KS4 Electricity – Static electricity


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Charge

Particle Charge

Proton

Neutron

Electron

+1

none

-1


Charge, attraction and repulsion


Attraction and repulsion

Positive and positive ________

Negative and negative ________

Positive and negative ________

repel

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:

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.


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?

+ ++ +


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.


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


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


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.


+ - + - + -

+ - + - + -

+ - + - + -

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


Uses of static electricity

Uses of static electricity:

1. _______________

2. _______________

3. _______________

4. _______________

Spray-painting

Printers

Photocopiers

Pollutant-removers


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


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


+++

+ --

-

--

-

--

-

-

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


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


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?


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


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?


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)


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


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!!!


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)


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


Formula triangles


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


What is the charge on an electron?

A. Positive

B. Negative

C. Neutral

D. Depends upon the atom


What force can be used to charge insulators?

A. Gravity

B. Friction

C. Weight

D. Energy


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


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


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

Download - © Boardworks Ltd 2003 KS4 Electricity – Static electricity

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