Electrical Principles

There are two main types of energy: kinetic and potential.

Kinetic energy is energy of motion.Any object or particle that is moving has kinetic

energy. http://www.youtube.com/watch?v=2MkAZu6QW0I

Potential energy is stored energy. Any object or particle that has energy but is not using

it has potential energy. http://www.youtube.com/watch?v=pNl8flwGWD8

The unit of energy is the Joule (J).

http://www.youtube.com/watch?v=8abzpXCjyjA&feature=PlayList&p=8F4E5BB40872CB7E&index=0&playnext=1

Other Types of Energymechanical energy- the combined total

of kinetic and potential energieschemical energy- a type of potential

energy; the energy stored in the bonds of molecules

thermal energy- a type of kinetic energy; the energy of vibrating particles in a material

electrical energy- a type of potential energy; the energy carried by charged particles

Energy TransferAn electric motor is used to turn

something. It converts electrical energy to mechanical energy.

A generator produces electricity. It converts mechanical energy to electrical energy.

A thermocouple produces electricity. It converts thermal energy to electrical energy.

A cell/battery produces electricity. It converts chemical energy to electrical energy.

http://www.youtube.com/watch?v=E69-RSok2TQ

Electrical Storage DesignElectrochemical cell: a package of chemicals

designed to produce small amounts of electricity e.g. a battery.

Dry cell- converts chemical energy to electrical energy.

Two electrodes (two different pieces of metal) and an electrolyte (a conducting solution).

Charges leave the negative electrode, pass through the electrolyte, and return to the positive electrode.

Called dry cells because the electrolyte is like a paste.

Wet cell- Same as above, but the electrolyte is a liquid that is usually an acid.

Salt bridge allows the exchange of ions.

http://www.youtube.com/watch?v=HlGITf-rhCE

http://www.youtube.com/watch?v=0oSqPDD2rMA

Dry cells and wet cells are both examples of primary cells. The reaction cannot be reversed, and as a result, the cells can only be used once.

Rechargeable cells are known as secondary cells. Two examples of rechargeable cells are Ni-Cd and Nickel metal-hydride.

Electric motors2 types: AC and DCMotors need energy to make a coil of wire spin

between a magnetArmature: rotating coil of wireElectromagnet: a coil of wire wrapped around

a magnetCommutator: a metal “switch” with split ringsAn electromagnet will move to line up with the

magnetic field of a nearby permanent magnetTo keep the electromagnet spinning, motors use

a commutator (split ring) and brushes. http://www.youtube.com/watch?v=it_Z7NdKgmY http://www.youtube.com/watch?v=Xi7o8cMPI0E

DC MotorElectrons flow from the battery to the

commutator and then armature, North is repelled by North and attracted to South

The armature begins to rotateAs the armature passes the field magnets,

current is cut off, the armature continues to spin because of momentum.

The commutator then reconnects! The commutator reverses the current in the

armature and the polarity of the magnetsMP3s, cell phones, computers, calculators

Electric DC Motor

A)

-Electrons flow to the right from the battery to the commutator into the armature. -North pole of armature is repelled by the top of the field magnet and attracted by the bottom of the field magnet. - Armature begins to rotate clockwise.

B)

-The commutator cuts off the current so the armature does not stall. - Armature keeps spinning due to momentum.

C)

-The commutator reverses the direction of current through the armature and polarity of magnets.- This allows armature to keep spinning.

AC MotorFound in dishwashers, washing machines,

garage door openers, furnacesRotating core or rotorStationary component or stator The motor functions based on magnetic

attraction and repulsion.

AC Electric Motor

-Operate on alternating current. - They have a rotating core, or rotor that is held in a laminated steel cylinder.

- Surrounding the rotor is a stationary component called a stator.

- Stator is a two pole (north and south) electromagnet.

- When the AC motor is turned on, the attraction and repulsion causes the rotor to spin.

Electric GeneratorElectric current is produced when a coil of wire rotates

inside a magnetAC generatorCoil of wire rotates inside a stationary field magnetThe coil rotates due to an external force ex. falling

waterAs the wire rotates, electrons move in 1 direction,

after half a turn, it passes the opposite magnetic poleThis makes the electrons (and the wire) rotate in the

opposite directionCar electrical systems http://www.youtube.com/watch?v=d_aTC0iKO68

Electrical Generator AC Generator (Alternating Current)- because current changes direction.

-Coil of wire rotates inside a stationary field magnet.

-The coil rotates due to an external force ex. falling water, steam, wind.

- Electric current is produced when a coil of wire is rotated inside a magnet.

- As the wire rotates, electrons move in 1 direction, after half a turn, it passes near the opposite magnetic pole. This makes the electrons rotate in the opposite direction

DC generator (dynamo)Armature connected to split ring

commutatorCurrent flows when the brushes touch the

metal ringsAt the gaps current flow (electron flow)

stopsThen the direction and the flow of charge

have reversed

DC Generators

There are several ways to change the speed at which the armature in a motor spins:increasing the strength of the magnets

increases the speed of the armatureincreasing the current increases the speed of

the armatureincreasing the number of coils of wire between

the magnets increases the speed of the armature

changing the orientation of the magnets so that like poles are against each other will stop the armature

Danger of Electrical DevicesThe voltage is the energy of individual charges. Total energy provides the danger, so a high

voltage does not present a significant danger if there are not a lot of charges (low current).

It becomes dangerous when the current (number of charges per second) is also increased to a high level, providing more overall energy.

To assess the danger of an electrical device, check the manufacturer’s label for voltage and current rating.

Remember that it is the combination of high voltage and high current that provides the danger.

http://www.youtube.com/watch?v=IEa04gZbWRU

SafetyNever handle electrical devices when you

are wet or near water unless they are specially designed and approved for use in wet areas.

Don’t use any power cord that is frayed or broken.

Always unplug electrical devices before looking inside or servicing them.

Don’t put anything into an electrical outlet other than proper plugs for electrical devices.

Don’t overload circuits by plugging in and operating too many devices.

Stay away from power lines.Don’t bypass safety features

built into home wiring, appliances, and other electrical devices.

When unplugging a device, pull on the plug, not on the electrical cord.

Never remove the third prong from a three-prong plug.

Static and CurrentStatic electricity- the build-up of electric

charges (protons and electrons are not equal!). Electrons flow from one object to another, making one positive charge and the other negative overall (due to rubbing or touching).

Charged objects cause charge separation when they are brought close to neutral objects.

e.g. the build-up of charges in your hair when you put a wool sweater on; these charges are transferred from the wool to your hair

e.g. lightening results from a build-up of charges in clouds; when the build-up becomes to large, the charges jump (discharge) to the ground

Electric Discharge When something has a build up of electric charges,

getting rid of that charge is “discharging it.” For example, two metal plates near each other, but

not touching will build up equal and opposite amounts of charge when connected to a battery.

When the battery is disconnected the plate charges will remain.

The charges will move from one plate to the other so the number of positive and negative charges on each plate is equal and resulting in no net charge build up.

Sometimes the charge buildup is large enough that it will discharge thru the air and you see it as a spark.

http://www.youtube.com/watch?v=YFeFsw3Ht2c

Current electricity- the flow of electric charges; the more charges that flow per second, the higher the current.

In general, electrical current carries electrical potential energy which is used to operate electrical devices

e.g. Charges with electrical energy flow through a light bulb; the electrical energy from the charges is converted to light and heat

Conductors and InsulatorsElectrical conductor- a material that allows

charges to flow through it; some materials are better conductors than others in that they allow charges to flow easier

e.g. Most metals are good conductors; copper is a very good conductor and is used to carry charges through your house, while nichrome wire conducts charges but not as well.

Superconductor – almost no resistance to electron flow, used in power lines and super computers.

Some materials become Superconductors in low temperatures.

eg. Mercury at absolute zero.

Electrical insulator- a material that does not allow charges to flow through it; insulators offer resistance to the flow of electric charge.

If something is a good insulator, it is a poor conductor.

e.g. rubber, plastic, cotton, glass, pure water

Resistance- something that hinders the motion of electric charge and converts electric energy into other forms of energy such as light, heat, and sound.

Symbol is R and units are Ohms ().e.g. filament in a light bulb generates heat

due to resistancee.g. lie detectors – measures skin resistance

because sweat is a salty and conductive solution

As wire length increases, resistance increasesAs temperature increases, resistance

increasesAs area decreases, resistance decreases

Resistance cont. Resistance is the friction in an electrical

circuit that controls the flow of current. Voltage is the pressure pushing on the

electrons in a circuit.

Why do we need resistance?

- Not enough resistance? - Too much resistance? - Exactly enough resistance?

Not enough Resistance IF we use a 6 Volt battery and a bulb that

is intended for 1 ½ Volts, the pressure is too high and the filament resistance allows too much current to flow. We get a single bright flash as the bulb burns out!

Too much Resistance If we use a 1 ½ Volt battery and a bulb

that is intended for 6 Volts, the pressure is too low and the filament resistance allows very little current to flow. The battery lasts for a very long time but the bulb is too dim to be of much use.

Exactly Enough Resistance When we use a 1 ½ Volt battery and a bulb

that is also intended for 1 ½ Volts, the current is just right. The bulb is bright, but it doesn’t burn out, and the battery lasts for quite a while.

Electrical FlowSwitch- something that will start or stop

electric currentResistor- something that resists the flow of

electric charge, takes electrical potential energy from charges and converts it to some other type of energy (light, heat, sound, etc)

Rheostat- a resistor whose resistance value can be changed

Nichrome wire has a high resistance, adding more nichrome wire to a circuit will increase the overall resistance.

Taking nichrome away will decrease the overall resistance.

VoltagePotential difference: the difference

in energy per unit of charge between one point in the circuit and another point.

The energy of an individual charge.

The symbol for voltage is the letter V and the units are Volts (V).

Volts are measured with a voltmeter.

Pretend an electric circuit is a race track. Each car represents a charge. Each car has a certain amount of gasoline that provides its energy.

The gasoline that each car has would represent the voltage.

The number of cars that pass by the starting line every second would represent the current.

As cars (charges) go up hills (resistors), each one uses up gasoline (voltage).

Each car needs to get more gasoline (voltage) at the pit stop (battery).

CurrentAmperage- a measure of

the strength of electric current.

The symbol for amperage is the letter I and the units are Amps (A).

Amperage is measured with an ammeter.

Smaller currents are measured with galvanometers.

Ohm’s law shows the relationship between voltage across a resistor (the energy that each charge loses across the resistor), the current through the resistor (the amount of charges that are flowing through the resistor each second), and the resistance of the resistor.

Resistance: Ohms Law Shows the relationship between voltage,

current and resistance.

1.Given a fixed resistance, more voltage causes more current.

2.Given a fixed voltage, more resistance causes less current.

Ohm’s law can be written as a mathematical equation:

e.g. An electric dryer draws an electric current of 22 A. The voltage drawn by the dryer is 220 V. What is the resistance of the dryer?

Given: I=22 A V=220 VFind: R = ?

1022

220

A

V

I

VR

TRY THESE ! Suppose that our bulb has a resistance of 50

ohms and we know that is should be used with a current of 0.03 amps. What battery voltage is needed?

Now supposed that we have a 3 Volt battery and that our bulb has a resistance of 100 ohms. How much current is flowing when the bulb is lit?

Now suppose that we have a 4.5 V battery and that there is 0.03 Amps of current flowing. What is the bulb resistance?

1.5 V, 0.03 amps, 150 ohms.

Photoelectric CellA photoelectric cell uses light to emit

electrons. These electrons can go around an electric circuit and power devices.

The burglar alarm uses a beam of UV light to cause electrons to be emitted from the photoelectric cell, causing the iron to become magnetized.

This magnetized iron attracts the switch from the second circuit, breaking that circuit, preventing the alarm from sounding.

When the burglar breaks the beam of UV light, no electrons flow in the first circuit so the iron loses its magnetism. The switch from the second circuit falls closed, completing the second circuit, causing the alarm to sound.

An electrical circuit is a system made up of 4 subsystems:

1. Source – cell or battery2. Conductor – wire3. Control – switch4. Load – lamp/motor

http://www.youtube.com/watch?v=E8AZBR8Zz04

The following is a list of symbols used when drawing electric circuit diagrams.

Series CircuitA series circuit is when the current passes

through each load in the circuit. In a series circuit there is only one path for the current to pass through.

A parallel circuit has more than one path, so current does not necessarily pass through each load. In this case, it one path is broken there is still at least one other path for current to come through.

Summary Series circuits are basic types of electrical circuits

in which all components are joined in a sequence so that the same current flows through all of them.

Parallel circuits are types of circuits in which the identical voltage occurs in all components, with the current dividing among the components based on their resistances, or the impedances.

In series circuits, the connection or circuit will not be complete if one component in the series burns out.

Parallel circuits will still continue to operate, at least with other components, if one parallel-connected component burns out.

Microelectronic CircuitsThe similarity between household circuits and

microelectronic circuits is that they perform the same basic function: to power an electrical device.

The primary difference between household circuits and microelectronic circuits is the scale.

Household circuits are on a much bigger scale. In a typical house, you might have dozens of electrical components.

On a typical microelectronic (integrated circuit), there may be millions of transistors(acts as a switch) and resistors. Microcircuit a circuit on a small scale.

Forms of Energy Inputs and Outputse.g. lightbulb- the input energy is electrical,

the output energy is light and heat.e.g. cd player- the input energy is

electrical, the output energy is sound (and also kinetic as the disc spins)

Energy TransformationsPower- the rate at which a device converts

energy. The symbol is P and the units are Watts

(W). 1 Watt is equal to 1.0 J/s.There are two equations that describe

power relationships:P = IV and E = Pte.g. A 100 W light bulb is plugged into a 120 V

outlet and is on for 5 minutes.

What is the current?Given: P=100 W V=120 V

t=5 minutes = 300 seconds

What is the energy used?

AV

W

V

PIIVP 83.0

120

100

JsWPtE 30000)300)(100(

The law of conservation of energy states that energy cannot be created or destroyed, but that it can be transformed from one type to another.

Efficiency refers to the percentage of original energy (input) that remains after an energy conversion (output).

No device is 100% efficient. This does not mean that energy is destroyed; it was simply converted to an another unusable form such as heat.

e.g. A light bulb uses electrical energy input to produce light.

The conversion is not 100% efficient. Some of the energy is lost in the form of heat.

Note that no energy was destroyed!! Efficiency Equation

%100__

__% x

inputenergytotal

outputenergyusefulEfficiency

e.g. A light bulb uses 780 J of electric energy, but produces only 31 J of light energy. What is the efficiency of the light bulb?

Given: Useful energy output=31 JTotal energy input=780 J

Find: % Efficiency

%9.3%100780

31%100

__

__% x

J

Jx

inputenergytotal

outputenergyusefulEfficiency

Reducing Energy Wastepick appliances that are

energy efficient (they have energy labels on them)

don’t leave lights on when not in the room

do full loads of laundry and dishes

improve bearings and lubricants in devices to reduce friction

add more insulation around stoves, refrigerators, and walls

Energy SourcesRenewable source- a source of energy that

can replenished naturally in a relatively short period of time

Tides- moving water from tides turn turbines that run generators.

There are not a lot of tidal power stations in the world because of the difficulty in finding a suitable location.

Environmentally friendly source of energy. Dams: Hydro-electric plants like those near

Niagara Falls, capture the energy of falling water. When water falls over the damn, it drives a generator, producing energy.

http://www.youtube.com/watch?v=1cysaOnlv_E http://www.youtube.com/watch?v=F3TUTfy1n60

Wind- use the wind to turn a turbine and run a generator

Modern windmills are more efficient than older ones because of the propeller shaped blades.

Not particularly efficient, but are environmentally friendly.

Usually grouped together in wind farms, such those in Pincher Creek.

Sunlight- uses the Sun to generate electricity

Modern technologies have made sunlight a more efficient way of producing current.

Solar cells are now used in many applications, including calculators and spacecraft and the International Space Station.

Environmentally friendly.Solar technologies can be either passive or

active depending on the way they capture, convert and distribute sunlight.

Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs.

Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun.

Batteries – Convenient source of electricity for portable devices, but they only produce energy after being charged using electricity from an external source.

They actually use more energy than they produce!

Non-renewable source- energy that cannot be replenished naturally in a relatively short period of time.

Such as fossil fuels: coal, oil, and natural gas. Fossil fuels are a reasonable choice in areas

that have large deposits that are easy to excavate.

Mining coal or tapping into deposits of oil and natural gas is only the first step in refining fossil fuels in order to generate electricity from fossil fuels.

Not environmentally friendly. http://www.youtube.com/watch?v=vBbhfQ1kDfw http://www.youtube.com/watch?v=fjgdgAhOzXQ

Air Pollution from Fossil FuelsFly ash : When coal is burned fly ash is

released into the air. Fly ash contains mercury, a poisonous metal that can damage the nervous system.

sulphur dioxide: has been identified as causing acid rain

nitrogen oxides: major cause of air pollution and acid rain

carbon dioxide: has been identified as causing global warning

Strip-miningUsed when deposits

are near the surface. Coal is often mined

using this method, and the coal can be used to generate electricity.

This type of mining removes all plants and animals from the area. The natural environment is never fully restored.

Oil and gas fired generators

Oil or gas is burned to heat water, which becomes steam and turns a turbine to generate electricity.

This process releases poisonous gases and warm water into nearby lakes and rivers.

There is a need to monitor plants and animals in the area to ensure their health.

Oil is pumped from wells, sometimes by injecting water into the ground. A significant amount of fresh water goes into the ground, out of the water cycle forever. Natural gas wells produce sour gas which is poisonous.

Technologies Based on ElectricityComputers

may make tasks more time efficient, more instant communication

lots of waste produced when computers are discarded

Cell PhonesInstant communication of words and picturesPeople are always reachable

Lasersused in cd players, medical applications such as

surgeries, dental work, communicationthe cost can be downside, although the cost is

decreasing

In general, many people would argue that technology had made our lives easier. Some would argue, however, that we are experiencing an information overload and are working harder than ever as a result of technology.

Electrical Technology IssuesConcerns

shrinking natural resource reservesincreasing demand on natural resourcesenvironmental concerns with the means in which

resources are obtained, used, and discardedSome ways to improve the sustainability of

energy use:manage resources according to what we have

rather than what we useimprove the efficiency of machines and

appliancesuse more renewable sources of energy, and

avoid the use of non-renewable energy sourcesmake good personal choices