Electricity 1Electricity 1

ElectrostaticsElectrostatics

andand

Current ElectricityCurrent Electricity

Aim of the lessonAim of the lesson

Static charge Static charge 3.6.26 recall that insulating materials can be 3.6.26 recall that insulating materials can be

charged by friction and explain this in terms of charged by friction and explain this in terms of transfer of charge.transfer of charge.

3.6.27 identify that positively charged objects 3.6.27 identify that positively charged objects have a deficiency of electrons and negatively have a deficiency of electrons and negatively charged objects have a surplus of electrons.charged objects have a surplus of electrons.

3.6.28 describe the dangers and use of 3.6.28 describe the dangers and use of electrostatic charge generated in everyday electrostatic charge generated in everyday contexts.contexts.

Text Book ReferenceText Book Reference

Physics CCEA pg 109-113Physics CCEA pg 109-113 ElectrostaticsElectrostatics is the study of charges at is the study of charges at

restrest

Sir Ben FrankSir Ben Frank

Fly that kite…Fly that kite…

ElectrostaticsElectrostatics

The organisation of the parts of an atom The organisation of the parts of an atom has has electronselectrons orbiting a large central orbiting a large central nucleus of nucleons (neutrons and nucleus of nucleons (neutrons and protons)protons)

neutral atom positive ion negative ion

These models are NOT to scale

If there is an unbalanced number of If there is an unbalanced number of protons (positive carriers) compared to protons (positive carriers) compared to electrons (negative carriers) then the ion is electrons (negative carriers) then the ion is called a called a charged particlecharged particle

3 electrons, 3 protons- no charge

2 electrons, 3 protons- positive charge (deficiency of

electrons)

4 electrons, 3 protons- negative charge

(surplus of electrons)

-

-- --

- -

--

+++ ++ ++

+ +

Charging by friction

The wool and polythene are each ‘uncharged’.

What does this mean?

In this diagram:

Charging by friction

The wool is ‘uncharged’,because…

…it has equal amounts of positive and negative charge.

Equal numbers of + and −

On the wool

+ − +

+ −− + −

−+ +− −

+

+

−

+

−

−

+

On the polythene

Charging by friction

Equal numbers of + and − on the wool:

(Count them!)

7 + 7 −

Equal numbers of + and − on the polythene:(Count them!)

3 + 3 −

+ − +

+ −− + −

−+ +− −

+

+

−

+

−

−

+

Charging by friction

If you rub the wool on the polythene, some electrons (−) move from the wool to the polythene.There are now more + than − on the wool:

(Count them!)

+ − +

+ − +

−+ +

− +

+ −

−

+−

−

− −

+

So now the wool is charged positively,with a surplus of 3 +

Charging by friction

What has happened to the polythene?

There are now more − than + on the polythene:(Count them!)

+ − +

+ − +

−+ +

− +

+ −

−

+−

−

− −

+So now the polythene is charged negatively,with a surplus of 3 −

Charging by friction

Both objects are equally charged,

with opposite charges

because electrons − (only) have moved from the wool to the polythene.

This is summed up in the diagram-

The overall effect of these charged particles The overall effect of these charged particles produces a produces a forceforce

If the electrical charge is ‘held’ on the If the electrical charge is ‘held’ on the surface of a material it is referred to as surface of a material it is referred to as static electricitystatic electricity..

This type of charge This type of charge cannot movecannot move through through out the material (out the material (an insulatoran insulator))

Charged objects exert an Charged objects exert an electrical force-electrical force- similar charges similar charges repelrepel each other and each other and opposite charges opposite charges attractattract..

The electrical static charge can be produced The electrical static charge can be produced in two ways- by in two ways- by frictionfriction and by and by induction. induction.

The The attractive forcesattractive forces which keep the which keep the electrons (electrons (negativenegative) close to the nucleus ) close to the nucleus ((positivepositive) can be easily overcome.) can be easily overcome.

The electrons have relatively The electrons have relatively low masslow mass compared to the nucleons and therefore it is compared to the nucleons and therefore it is only ever the only ever the electrons which can be electrons which can be transferredtransferred throughout a material or from throughout a material or from one material to another.one material to another.

Everyday examples of Everyday examples of electrostatic electrostatic

Lightning-Lightning- the bottom of a cloud can be the bottom of a cloud can be

charged by friction of other air particles tocharged by friction of other air particles to

produce a large negative produce a large negative electrostatic charge. electrostatic charge. This can be discharged This can be discharged on the positively charged on the positively charged upper surface of another upper surface of another cloud or the positively cloud or the positively charged ground.charged ground.

Page 111 and 112Page 111 and 112

+ + + + +

++++

- - - - - - -

Electrically conductive truck tyres-Electrically conductive truck tyres- These tyres drain any charge built up by These tyres drain any charge built up by passing air particles. This safety feature passing air particles. This safety feature stops any sparks occurring which might stops any sparks occurring which might prove explosive for any trucks carrying prove explosive for any trucks carrying large amounts of fuel.large amounts of fuel.

Air Purification-Air Purification- Industries release a huge Industries release a hugeamount of air pollutants into the atmosphere. amount of air pollutants into the atmosphere.

25000 V 0 V

Electrons repelled

Positives fixed

Dust particle

Some of the fine Some of the fine dust can be dust can be eliminated by eliminated by passing the passing the exhaust through exhaust through charged charged electrostatic plates electrostatic plates which attract the which attract the charged smoke charged smoke particlesparticles

+

+

+

+

+

+++

Aims of the lessonAims of the lesson

Charge flow Charge flow 3.6.29 understand that an electric current is a 3.6.29 understand that an electric current is a

flow of electrons and that it is in the opposite flow of electrons and that it is in the opposite direction to that of a conventional current.direction to that of a conventional current.

3.6.30 3.6.30 recall that charge is measured in recall that charge is measured in coulombs.coulombs.

3.6.31 3.6.31 recall and use the quantitative recall and use the quantitative relationship between current, charge and relationship between current, charge and time.time.

FactoidsFactoids

The charge on one Electron is

1.60 x 10-19 C

0.000 000 000 000 000 000 160 Coulombs

There are roughly 1 x 1021 electrons in a 1 m length of metal wire

~1 000 000 000 000 000 000 000 electrons

Current flow within a Current flow within a circuitcircuit The flow of electricity in a circuit is due to the The flow of electricity in a circuit is due to the

charge, Q,charge, Q, moving within the material (copper moving within the material (copper wires). wires).

The speed of the flow is known as the The speed of the flow is known as the currentcurrent (symbol I) (symbol I)

This is similar to the flow of water in a river being This is similar to the flow of water in a river being called a current- when it flows fast there is a called a current- when it flows fast there is a strong current.strong current.

Current DefinitionCurrent Definition

Electrical Current is the rate of flow of Electrical Current is the rate of flow of charge past a given point in a circuitcharge past a given point in a circuit

How fast or the time it takes…

The number of charged particles

Current = Charge / Time

I = Q / t

Amps = Coulombs / Seconds

Symbol Equation

Units Equation

Electrical CurrentElectrical Current

Reference Page 114Reference Page 114

Circuit DiagramsCircuit Diagrams

Page 115Page 115 3.6.34 describe and record 3.6.34 describe and record

diagrammatically simple electric circuits.diagrammatically simple electric circuits.- Draw a circuit diagram of the circuit Draw a circuit diagram of the circuit

which is set up by Mr McClellandwhich is set up by Mr McClelland- A simpler way of representing a circuit A simpler way of representing a circuit

visually is using the set of visually is using the set of electrical electrical circuitcircuit symbolssymbols to represent each to represent each componentcomponent.. (make sure you know them!) (make sure you know them!)

Draw the circuitDraw the circuit

SwitchVoltmeter in parallel over a bulb

Two Bulbs in parallel

A

V

Conventional Flow v Electron FlowConventional Flow v Electron Flow Page 114-Page 114- Electrical Electrical

current is current is conventionallyconventionally known known as flowing from the as flowing from the positive terminalpositive terminal to to the the negative terminalnegative terminal..

However, we refer to However, we refer to the the electrons aselectrons as flowing flowing from the from the negative negative to the to the positivepositive due to the due to the attractionattraction that the that the negative charge has negative charge has to the positive to the positive terminal.terminal.

ConductorsConductors- The electrons are free to - The electrons are free to move within these materials, very little move within these materials, very little energy is required to free the electrons energy is required to free the electrons from their atoms. (Metals, carbon)from their atoms. (Metals, carbon)

InsulatorsInsulators- Charge cannot move through - Charge cannot move through these materials as they have very few these materials as they have very few free electrons. (Plastics, ceramics, free electrons. (Plastics, ceramics, rubber)rubber)

The Movement of The Movement of ElectronsElectrons

Experiment- Electrical Experiment- Electrical CurrentCurrent

Set up the following circuits and find the Set up the following circuits and find the electrical current flowing at each point electrical current flowing at each point indicated.indicated.

Series

Parallel

+

ResultsResults

TableTable Point on the circuit Current (A)

0.250.25

0.250.25

0.50.50.250.25

0.250.25

ConclusionConclusion

The The ammeterammeter measures the measures the current current flowing in the circuitflowing in the circuit as the electrons as the electrons pass through it. pass through it.

For a For a series circuitseries circuit the electrical current the electrical current will be will be the same at every pointthe same at every point

For a For a parallel circuitparallel circuit the current entering the current entering the parallel section the parallel section will be equal to the will be equal to the sum of thesum of the current of the branches of the current of the branches of the parallel section (currentparallel section (current splits splits))

Extra Syllabus Reference-Extra Syllabus Reference-

3.6.36 recall that in a series circuit the 3.6.36 recall that in a series circuit the current is the current is the same everywheresame everywhere..

3.6.38 recall that in a parallel circuit the 3.6.38 recall that in a parallel circuit the sum of the currentssum of the currents in the branches is in the branches is equal to the current enteringequal to the current entering the parallel the parallel section.section.

So eh, what’s the So eh, what’s the current?current?

Series-Series- Parallel-Parallel-

+

Current the same everywhere!! Current into the junction is

equal to the current out

Examples of current in a Examples of current in a circuitcircuit

What is the reading on each of the What is the reading on each of the following ammeters-following ammeters-

3A

A1

A2

A3

Bad Parents…Bad Parents…