Basic ElectricityBasic Electricity

DC and ACDC and AC

What is Electricity?What is Electricity?

Electricity is a general term used for Electricity is a general term used for the presence and flow of the presence and flow of electric chargeelectric charge . .

In more scientific terms, it is the flow In more scientific terms, it is the flow of electrons from one place to of electrons from one place to another.another.

Types of ElectricityTypes of Electricity

Static – Metal door handles on cold Static – Metal door handles on cold dry mornings (OUCH!)dry mornings (OUCH!)

Stored – Batteries, etc.Stored – Batteries, etc.Generated- Provides our homes and Generated- Provides our homes and

schools with power.schools with power.All deal with the flow of electrons All deal with the flow of electrons

from one point to another.from one point to another.

Electrons?Electrons?

As we know, an atom is made up of As we know, an atom is made up of sub-particles, those being:sub-particles, those being:ELECTRONS (negatively charged)ELECTRONS (negatively charged)PROTONS (positively charged)PROTONS (positively charged)NEUTRONS (neutral, no charge)NEUTRONS (neutral, no charge)

ELECTRON (-)

PROTONS (+) &

NEUTRONS (0)

Electron FlowElectron Flow

To illustrate the most basic form of To illustrate the most basic form of electron flow, we use something electron flow, we use something called a circuit.called a circuit.

The circuit is made up of a The circuit is made up of a power power sourcesource, , conductorsconductors (wires) to provide (wires) to provide a path for the electrons to flow, and a path for the electrons to flow, and a useful device such as a light bulb a useful device such as a light bulb (also called a (also called a LOADLOAD))

The Basic CircuitThe Basic Circuit

NEGATIVE ( - ) POSITIVE (+)

Electrons flow NEGATIVE to POSITIVE

The Circuit Shown Here is aThe Circuit Shown Here is aDC (Direct Current) CircuitDC (Direct Current) Circuit

In a DC Circuit, there is only ONE direction for current flow.

Note the switch opens, current stops flowing.

DC Circuits

Direct Current is provided to us mostly by batteries, used in :

– Flashlights– iPods– Laptop Computers– Automobiles– Solar Cells

DC Series Circuits

Loading batteries in a flashlight is a good example.

Batteries are placed end to end, positive to negative.

+ + +_ _ _

1.5 volts 1.5 volts 1.5 volts

Batteries in Series

When batteries are installed this way, they are said to be AIDING one another.

If three 1.5 volts batteries were installed in a flashlight, what would the total voltage be ?

3 X 1.5 = 4.5 volts

Parallel

If batteries are connected in parallel, something completely different happens.

A good example of this is connecting jumper cables between car batteries.

A car battery is 12 volts. If the cables were hooked up in SERIES,

12 + 12 = 24 volts, and the starter would be TOAST!

Parallel Circuits

Instead, Positive is connected to Positive. Negative is then connected to Negative. The voltage remains at 12 volts – it does not increase. What DOES increase is the amount of electrical current

to turn over a weak starter.

Series vs. Parallel

Each have their use SERIES increases voltage (add voltages) PARALLEL increases current.

SERIES- 3 bulbs drop 4 SERIES- 3 bulbs drop 4 volts each to divide the load. volts each to divide the load. 3 times 4 = 12. 3 times 4 = 12.

PARALLEL – 12 volts is present PARALLEL – 12 volts is present EVERYWHEREEVERYWHERE in the circuit in the circuit

WHAT IF A BULB GOES OUT IN EITHER WHAT IF A BULB GOES OUT IN EITHER SITUATION? WHAT WILL HAPPEN TO SITUATION? WHAT WILL HAPPEN TO THE OTHER BULBS?THE OTHER BULBS?

AC CurrentAC Current

A more complicated type of current is A more complicated type of current is AC, or Alternating Current.AC, or Alternating Current.

Like DC, it involves the movement of Like DC, it involves the movement of electrons.electrons.

Unlike DC, AC electrons move in one Unlike DC, AC electrons move in one direction, then they reverse.direction, then they reverse.

This means that current flows one This means that current flows one way, then the other.way, then the other.

ACAC

AC power is provided to us by our AC power is provided to us by our electric company.electric company.

Without it, life would be rather dull Without it, life would be rather dull (and DARK)(and DARK)

AC powers just about everything in AC powers just about everything in our homes that use electricity.our homes that use electricity.

When you plug a power cord into a When you plug a power cord into a wall outlet, you are using AC.wall outlet, you are using AC.

AC – Alternating CurrentAC – Alternating Current

AC is created by a device called a AC is created by a device called a generator (or ALTERNATOR)generator (or ALTERNATOR)

As a result of magnetic field being cut by a As a result of magnetic field being cut by a conductor, AC is produced.conductor, AC is produced.

AC in its simplest form is represented by AC in its simplest form is represented by something called a SINE WAVE…….something called a SINE WAVE…….

The AC Sine WaveThe AC Sine Wave

How The Sine Wave Is How The Sine Wave Is ProducedProduced

The SINE WAVEThe SINE WAVE

This drawing represents how a sine wave looks when viewed through an oscilloscope

0 dg

90 dg

180 dg

270 dg

360 dg180

Producing AC Sine WavesProducing AC Sine Waves

Electrical Waveforms

Alternating current or voltage

Pulsating direct current or voltage

Fluctuating direct current or voltage

Basic GeneratorBasic Generator

Generating A Sine Wave

N

S

Motion is parallel to the flux. No voltage is induced.

0

degrees

x

Generating A Sine Wave

N

S

Motion is 45 to flux. Induced voltage is 0.707 of maximum.

x

Generating A Sine Wave

N

S

Motion is perpendicular to flux. Induced voltage is maximum.

90 degrees

x

Generating A Sine Wave

Motion is 45 to flux.

N

S

Induced voltage is 0.707 of maximum.

Generating A Sine Wave

N

S

Motion is parallel to flux. No voltage is induced.

180

degrees

x

Generating A Sine Wave

Motion is 45 to flux.

N

S

Notice current in the conductor has reversed.Induced voltage is 0.707 of maximum.

Generating A Sine Wave

N

S

x

Motion is perpendicular to flux. Induced voltage is maximum.

270

degrees

Generating A Sine Wave

N

S

x

Motion is 45 to flux. Induced voltage is 0.707 of maximum.

Generating A Sine Wave

Motion is parallel to flux.

N

S

No voltage is induced.

Ready to produce another cycle.

360

degrees

BECAUSE OF ITS VERSATILITYAC IS EASIER TO GENERATEAC IS EASIER TO TRANSMITAC IS EASIER TO STEP-UP OR DOWNAC IS MORE ECONOMICAL

WHY AC ?WHY AC ?

Producing ACProducing AC

AC GENERATING STATIONS USE A AC GENERATING STATIONS USE A VARIETY OF METHODS TO PRODUCE VARIETY OF METHODS TO PRODUCE ELECTRICITYELECTRICITY

HYDROELECTRIC HYDROELECTRIC STEAMSTEAMCOALCOALNUCLEAR…..ARE MEANS OF NUCLEAR…..ARE MEANS OF

OPERATING THE TURBINES THAT OPERATING THE TURBINES THAT PRODUCE THE ELECTRICITYPRODUCE THE ELECTRICITY

Generating ACGenerating AC

THE VOLTAGE THAT LEAVES THE THE VOLTAGE THAT LEAVES THE GENERATING STATION IS VERY HIGHGENERATING STATION IS VERY HIGH

APPROX. 275,000 VOLTS OR MOREAPPROX. 275,000 VOLTS OR MORETHE ELECTRICITY MUST BE STEPPED THE ELECTRICITY MUST BE STEPPED

DOWN BEFORE POWERING OUR DOWN BEFORE POWERING OUR HOMESHOMES

HOUSEHOLD CURRENT IS 120/240 HOUSEHOLD CURRENT IS 120/240 VOLTS AT 60 HERTZVOLTS AT 60 HERTZ

TRANSFORMERS ARE USED TO STEP TRANSFORMERS ARE USED TO STEP DOWN VOLTAGE FROM HIGH TO LOWDOWN VOLTAGE FROM HIGH TO LOW

TransformersTransformers

Other AC UsesOther AC Uses

AC IS USED IN TELECOMMUNICATIONSAC IS USED IN TELECOMMUNICATIONSAC SIGNALS ALLOW INTELLIGENCE TO AC SIGNALS ALLOW INTELLIGENCE TO

BE XMITTED OVER LONG DISTANCESBE XMITTED OVER LONG DISTANCESA XMITTING ANTENNA CONVERTS AC A XMITTING ANTENNA CONVERTS AC

SIGNALS INTO ELECTROMAGNETIC SIGNALS INTO ELECTROMAGNETIC WAVESWAVES

THE SIGNAL THAT REACHES RADIOS THE SIGNAL THAT REACHES RADIOS AND TV’S IS ACAND TV’S IS AC

More About ACMore About AC

AC is not only measured in VOLTS, but AC is not only measured in VOLTS, but also in a unit called the HERTZ.also in a unit called the HERTZ.

The HERTZ is a unit of measuring time, The HERTZ is a unit of measuring time, called FREQUENCY.called FREQUENCY.

The electricity in our houses makes 60 The electricity in our houses makes 60 complete cycles per second, therefore its complete cycles per second, therefore its frequency is 60 HERTZ.frequency is 60 HERTZ.

More Uses for ACMore Uses for AC

Sometimes AC power is all that is Sometimes AC power is all that is available, but you have a device such available, but you have a device such as a music player that operates on as a music player that operates on batteries.batteries.

What do you do ??????????????What do you do ??????????????

Converting AC to DCConverting AC to DC

By using a Power Supply, the AC wave is By using a Power Supply, the AC wave is cut in half and filtered so that it becomes cut in half and filtered so that it becomes smooth DC.smooth DC.

AC adapters perform this task.AC adapters perform this task.

120 VAC12 VAC

12 V DC

SAFETY FIRST !SAFETY FIRST !

When working around electricity, one When working around electricity, one must observe some basic precautions:must observe some basic precautions:Never work with electricity when wet.Never work with electricity when wet.Be careful that metal objects or liquids Be careful that metal objects or liquids

don’t come in contact with electricity.don’t come in contact with electricity.NEVER pour water on an electrical fire!!NEVER pour water on an electrical fire!!Try to use only one hand if at all possible.Try to use only one hand if at all possible.Electricity is something we can’t see (but Electricity is something we can’t see (but

can sure feel if we goof up!)can sure feel if we goof up!)

What did we learn?What did we learn?

What is the difference between AC and What is the difference between AC and DC?DC?

What is the difference between a SERIES What is the difference between a SERIES and a PARALLEL circuit ?and a PARALLEL circuit ?

What is a common household voltage?What is a common household voltage?

What is the basic AC wave called?What is the basic AC wave called?

The EndThe End