Where does electricity come from?

Where does electricity come from?

A short “history” of the universe Around 14 Billion years ago there was nothing

No time – No space (really, nothing!) Just an enormous concentration of energy and heat – an

infinitely hot and dense fireball existing for ten trillion, trillion, trillionths of a second (10-36)

A fraction of a picosecond (10-12 ) later came the “Big Bang” (or “Big Whoosh” – no sound in space)

The “singularity” became a “plurality” (in science geek terms!) producing all the building blocks for “natures tricks”

At this point the universe began to cool into a melting pot of radiation, matter and anti-matter

The matter and anti-matter went to “war” and matter was the victour

The “survivors” represent around one-half of one percent of the original “combatants”!

The “birth” of the atom The original Big Bang “super

force” changed into 4 distinct forces:

Gravity Strong Nuclear Binding force Weak Nuclear force Electromagnetic force

These forces began to construct the material universe

Lots of “exotic” particles formed and were subject to the cosmic version of natural selection

The two lightest particles survived – quarks and Leptons

Quarks and Leptons Within 3 min. after the Big Bang

protons and Neutrons appear. Made up from Quarks Quarks come in 6 different

varieties. Quarks can only survive in

threesomes held together with “gluons”

“up-down-up” = Proton (positive charge)

“down-up-down” = Neutron (no charge)

Neutrons allow Proton to come together to form the nucleus of an atom.

Enter The Atom A few minutes after the Big Bang the

universe had cooled to around 1 billion degrees allowing atom nuclei to form.

When the universe cooled to around 3000 degrees a dense fog of electrons (negative charge) could be “captured” by the atom nucleus

Electrons formed by Leptons In a stable atom the number of

electrons equals the number of protons. Atoms with an excess of electrons are

“negative Ions” Atoms with a deficiency of electrons are

“positive Ions”

Static vs Current electricity

Static Current

The ancient Greeks observed that amber rubbed on a cloth attracts light particles

The electrons are removed from the cloth and added to the amber.

Creates Ions This imbalance creates electric

pressure which tries to restore the balance

The difference in charge is called “potential difference”

The discharge of this pressure is called “static electricity”

Two materials with an imbalance of electrons have a potential difference

When these materials are connected together by a conductor (metal) this allows the excess electrons equalise

When the two materials are at equal potential current flow ceases.

Usually obtained from “non-static” sources

These sources can either be: Direct Current (D.C.) Alternating Current (A.C.)

Sources of Current Electricity

Used to abbreviate large and small values of a “Standard Unit”

Can be easily converted to/from ENGINEERING NOTATION

Scientific notation is a less structured version of engineering notation.

Multiples and Sub-multiples

Actual Number 0.000000000001 0.000000001 0.000001 0.001

1000 1000000 1000000000 1000000000000

1 x 10-12

1 x 10-9

1 x 10-6

1 x 10-3

1 x 103

1 x 106

1 x 109

1 x 1012

Pico (p) Nano (n) Micro (µ) Milli (m)

Kilo (k) Mega (M) Giga (G) Tera (T)

Engineering Notation Unit prefix

Multiples and Sub-multiplesFor both scientific and engineering notation the power

or indices represents how many decimal places the decimal shifts; To the right for a positive number

3.67 x 1011 = 367000000000 To the left for a negative number

3.67 x 10-11 = 0.0000000000367

Named after Italian Allesandro Volta (1745 – 1851)

Discovered how to produce and Elecro-motive Force (EMF) from and electrical cell.

EMF – electrical pressure Equation symbol – V Unit – Volt (V)

The Volt

The Ampere (Amp) Named after Frenchman André

Marie Ampère (1775 – 1851) Mathematician and physicist,

considered the father of electrodynamics.

Current – flow of electrons in a conductor

Equation symbol – I Unit – Ampere or Amp (A)

The Ohm Named after German Georg Ohm (1789 –

1854) Determined that there is a direct

proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current – now known as Ohm's law.

Resistance – the opposition of current flow Equation symbol – R Unit – Ohm (Ω)

If the Resistance stays constant and the Electromotive force (voltage) is increased:

What happens to the current?

Results from experiments

If the Resistance stays constant and the Electromotive force (voltage) is increased:

What happens to the current? Current increases

Results from experiments

If the Resistance stays constant and the Electromotive force (voltage) is increased:

What happens to the current? Current increases

Results from experiments

I V

If the Resistance stays constant and the Electromotive force (voltage) is increased:

What happens to the current? Current increases

Results from experiments

I α V

If the Resistance in the circuit is decreased and the Voltage stays constant:

What happens to the current?

Results from experiments

If the Resistance in the circuit is decreased and the Voltage stays constant:

What happens to the current? Current increases

Results from experiments

If the Resistance in the circuit is decreased and the Voltage stays constant:

What happens to the current? Current increases

Results from experiments

I R

If the Resistance in the circuit is decreased and the Voltage stays constant:

What happens to the current? Current increases

Results from experiments

I α 1/R

Ohm’s Law states: states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.

Ohm’s Law

V = IR

1 Ω 2 Ω 3 Ω 4 Ω0

2

4

6

8

10

12Amps

Amps

Graph for a 10 Volt Supply

2 Volts 4 Volts 6 Volts 8 Volts0123456789

Amps

Amps

Graph for a 1Ω Resistor

NOW….. The Maths!!!

Quantity of Charge Q = I x t Where

Q = charge in Coulombs I = current in Amperes t = time in Seconds

1 Coulomb = 6.242 x 1018 electrons

Q

I t

Mechanical Units(A brief introduction into SI units)

FUNDAMENTAL UNITS

NAME SYMBOL UNIT (unit symbol)

Length l Metre (m)Time t Second (s)Mass m Kilogram (kg)

Current I Ampere (A)Temperature T Kelvin (K)Amount of a substance

Mol Mole (mol)

Luminous intensity

Iv Candela (cd)

Mechanical Units(A brief introduction into SI units)

DERIVED UNITS (defined by Fundamental Units)NAME SYMBOL UNIT (unit symbol) FORMULA

Distance and DISPLACEMENT

d (s) Metres (m) length

Area A Metres Squared (m2) length x width

Volume V (v) Metres Cubed (m3) length x width x height

Velocity v Metres per Second (m/s) d / t

Acceleration a Metres per Second squared (m/s2)

F / m

Force F Newton (N) m x aEnergy and Work W Joule (J) F x d

Power P Watt (W) W / tElectromotive Force V Volt (V) P / I

Length vs Distance vs Displacement

Length : how long an object is Distance : the total length of motion. (in

all directions) Displacement : the total length of

motion. (in a straight line “as the crow flies”)

Thickness (d) : how wide an object is.Radius (r) : the distance from the centre of a circle to the edgeDiameter (d) : the distance from one side of a circle to another.

Time – always expressed in seconds when expressed in a formula.

Mass – originally based on the weight of 1000 millilitres of water at 0º C now the mass of a platinum weight in the Louvre (Paris). (1kg)

Current – One ampere flows when one volt of potential difference is applied to a resistance one ohm or when one coulomb (6.25 x 1018 electrons) flows in a conductor for one second

Temperature – The Kelvin scale starts at absolute 0 (when all molecular movement ceases – minus 273ºC)

Time, Mass, Current, and Temperature

Generally Force = Mass x Acceleration F = ma

In free fall Force = Mass x Gravity F = mg g = 9.8 m/s2

Force

Energy is defined as the ability to do work

Energy (work) = Force x Distance

W = F x l 2 types – potential

and kinetic

Energy and Work

Power is the ability to do work Power = work / time P = W / t

Power

Electrical power is the work done by one volt potential and one amperePower = Voltage x CurrentP = V x I

Since P = V x I and V = I x R we can say: P = (I x R) x I or P = I2 x R

AND since P = V x I and I = V/R we can say: P = V x (V/R) or P = V2 / R

Power (cont.)

When current passes through a resistor the work done by the resistor is heat.

This heat is generally unwanted. This heat is generally express as I2R All electrical equipment has a power rating equal

to the maximum power dissipation. If the actual power dissipated is greater than this

rating then the component will be “cooked”!

Power Dissipationand Power Rating

Power can be measured by the product of values obtained from a voltmeter and ammeter.

Alternatively power can also be measured using a WATTMETER

Power Measurement

Examples of the Effects of electic current

I2R or Heat – when electricity flows through a conductor, work must be done to overcome the resistance. Work = Energy = Heat

Magnetic – A conductor carrying current will always have a magnetic field circulating around it. Work = motion

Chemical – the passage of electrons and ions can change the physical and/or molecular structure of matter.

Physiological – electric shock

The 4 main effects of electrical current

Can be useful when heat is a desired effect. (Room heating, melting materials, etc.)

Can be detrimental when heat is an undesired effect. (heating of cables, heat pollution)

Electrical Heating

The principal requirement of electrical conductors and cables is that they carry the required current without becoming too hot for safety.

In week one we learnt : The original Big Bang “super force”

changed into 4 distinct forces: Gravity Strong Nuclear Binding force Weak Nuclear force Electromagnetic force

The electromagnetic effect of current is interdependent with current flow

This effect is used in most electrical machines

Magnetic Effects of Current

Two different effects: Electrolysis Voltaic cells

Electrolysis is used in metal refining, battery charging and electroplating. It is also the cause of “galvanic action” (corrosion or rust)

Chemical effects of electric current

The Voltaic cell: Two main types – primary

and secondary A primary cell is made up of

two different metals immersed in an acidic or alkaline electrolyte (usually liquid)

A battery is made up of these electrical cells.

Anode – positive electrode Cathode – negative

electrode

Chemical effects of electric current cont.

The effects on the human body are related to:

The amount of current The current path The duration of current flow The type of circuit with which the contact is made The voltage of the circuit The resistance of the human body.

The Electrical Safety act makes compliance with the electrical standard (AS/NZS-3000:2007) mandatory.

Physiological effects of an electric current.

“Electrician’s Bible”

1.1 SCOPEThis Standard sets out requirements for the design, construction andverification of electrical installations, including the selection andinstallation of electrical equipment forming part of such electricalinstallations.These requirements are intended to protect persons, livestock, andproperty from electric shock, fire and physical injury hazards that mayarise from an electrical installation that is used with reasonable careand with due regard to the intended purpose of the electricalinstallation.In addition, guidance is provided so that the electrical installation willfunction correctly for the purpose intended

AS/NZS 3000:2007 – Wiring Rules

1.5 FUNDAMENTAL PRINCIPLES 1.5.1 Protection against dangers and

damageThe requirements of this Standard are

intended to ensure the safety of persons, livestock, and property against dangers and damage that may arise in the reasonable use of electrical installations.

AS/NZS 3000:2007 – Wiring Rules

1.5.1 Protection against dangers and damage cont.In electrical installations, the three major types of risk are as follows:(a) Shock current Shock current arising from contact with parts that are live in normal

service (direct contact) and contact with parts that become live under fault conditions (indirect contact).

(b) Excessive temperatures Excessive temperatures likely to cause burns, fires and

other injurious effects. Persons, fixed equipment, and fixed materials adjacent to electrical equipment shall be protected against harmful effects of heat developed by electrical equipment, or thermal radiation, particularly the following effects:

(i) combustion or degradation of materials;(ii) risk of burns;(iii) impairment of the safe function of installed equipment.

(c) Explosive atmospheres Equipment installed in areas where explosive gases or dusts may be present shall provide protection against the ignition of such gases or dusts.

AS/NZS 3000:2007 – Wiring Rules

Direct contact – Basic protection – contact with live parts under “normal” conditions

AS/NZS 3000:2007 – Wiring Rules

1.5.3 Protection against electric shock1.5.3.1 ScopeProtection shall be provided against shock

current arising from contact with parts that are live in normal service (direct contact) or parts that become live under fault conditions (indirect contact).

Therefore, live parts must not be accessible and accessible conductive parts must not be live, neither under normal conditions nor under single fault conditions.

AS/NZS 3000:2007 – Wiring Rules

1.5.4 Basic protection (protection against direct contact)1.5.4.1 GeneralProtection shall be provided against dangers that may arise from contact with parts of

the electrical installation that are live in normal service.1.5.4.2 Methods of protectionBasic protection shall be provided by one or any combination of thefollowing methods:(a) Insulation, in accordance with Clause 1.5.4.3.

(b) Barriers or enclosures, in accordance with Clause 1.5.4.4.

(c) Obstacles, in accordance with Clause 1.5.4.5.

(d) Placing out of reach, in accordance with Clause 1.5.4.6.

RCDs are not recognized as a sole means of basic protection againstcontact with live parts but may be used to augment one of the abovemethods.

AS/NZS 3000:2007 – Wiring Rules

Indirect contact – fault protection – contact with live parts under “fault” conditions

AS/NZS 3000:2007 – Wiring Rules

1.5.5 Fault protection (Protection against indirect contact)

1.5.5.1 GeneralProtection shall be provided against dangers that

may arise from contact with exposed conductive parts that may become live under fault conditions.

In each part of an electrical installation, one or more methods of protection shall be applied, taking account of the conditions of external influence.

The methods of protection applied in the installation shall be considered in the selection and erection of equipment.

AS/NZS 3000:2007 – Wiring Rules

1.5.5.2 Methods of protectionFault protection shall be provided by one or any combination of thefollowing methods:(a) Automatically disconnect the supply on the occurrence of a fault likelyto cause a current flow through a body in contact with exposed conductive parts, where

the value of that current is equal to or greater than the shock current, in accordance with Clause 1.5.5.3.

(b) Prevent a fault current from passing through a body by the use ofClass II equipment or equivalent insulation, in accordance with Clause 1.5.5.4.

(c) Prevent a fault current from passing through a body by electrical separation of the system, in accordance with Clause 1.5.5.5.

(d) Limit the fault current that can pass through a body to a value lower than the shock current.

NOTE: The most commonly used method of protection is automaticdisconnection of supply.

AS/NZS 3000:2007 – Wiring Rules

Mechanical

Chemical

Radiant

3 major sources of electricity

Electromagnetic – rely on a magnetic field and motion

Mechanical sources

Piezoelectric – compression of a crystal creates an electric current

Mechanical sources

Batteries – Primary 2 dissimilar metals in an electrolyte Instant charge – can’t be recharged

Chemical sources

Batteries – Secondary Requires initial charging - rechargeable

Chemical sources

Fuel cell Converts the chemical energy of a fuel

(hydrogen) and an oxidant directly to electricity

Chemical sources

l

Flow cell Similar to fuel battery – consumes 2 sets of

fuel: 1 +ve and 1 –ve (electrolytes) Can be recharged by replacing these

electrolytes

Chemical sources

Photoelectric Converts energy

from the sun (light) into electricity

Used to supply stand alone and grid connected power supplies

Radiant sources

Thermoelectric – converts heat energy to electrical

Uses a junction of 2 dissimilar metals to generate a voltage.

Output voltage is very small (mA and µA)

Radiant sources

Practical exercise 7.2 work book page 95 – Heating efficiency

No electrical system is 100% efficient therefore there will always be losses

Efficiency

Efficiency = outputInput

%Efficiency = output x 100Input

1

Heat (I2R) – almost unavoidable Accounts for the majority of losses in electrical

and mechanical systems. Sound – noise energy losses Light – usually a by-product of heat

Electrical Losses

The law of conservation of mass states that energy is neither gained or lost

The law of conservation of energy states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created or destroyed. The only thing that can happen with energy in an isolated system is that it can change form, that is to say for instance kinetic energy can become thermal energy. Because energy is associated with mass in the Einstein's theory of relativity, the conservation of energy also implies the conservation of mass in isolated systems (that is, the mass of a system cannot change, so long as energy is not permitted to enter or leave the system).

Another consequence of this law is that perpetual motion machines can only work if they deliver no energy to their surroundings, or if they produce more energy than is put into them without losing mass (and thus eventually disappearing), and are therefore impossible

Entropy is a function of a quantity of heat which shows the possibility of conversion of that heat into work.

Conservation of energy

From Wikipedia, the free encyclopedia

Standard Electrical Circuit Symbols

Cell Battery Connecting wire Junction

Crossing – no

junction

Fuse Lamp Voltmeter

Ammeter Switch

Source of Electricity

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection -

fuse

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection –

fuse Ammeter – in series

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection –

fuse Ammeter – in series Control device - switch

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection –

fuse Ammeter – in series Control device –

switch Load – what the

electricity is powering

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection –

fuse Ammeter – in series Control device –

switch Load – what the

electricity is powering Voltmeter – in parallel

Circuit Diagram for Practical Exercise

Source of Electricity Circuit Protection –

fuse Ammeter – in series Control device – switch Load – what the

electricity is powering Voltmeter – in parallel Connecting Wires

Circuit Diagram for Practical Exercise

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor