ELECTRICAL SYSTEMS 1 ELECTRICITY STANDARDS 5.1 Measure and calculate voltage, current, resistance, and power consumption in series and parallel circuits,

ELECTRICAL SYSTEMS

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ELECTRICITY STANDARDS5.1 Measure and calculate voltage, current, resistance, and power

consumption in series and parallel circuits, using the appropriate instrument.

5.2 Components of a circuit, including sources, conductors, circuit breakers, fuses, controllers, and loads. Examples of some controllers are switches, relays, diodes, and variable resistors.5.3 Relationships among voltage, current, and resistance in a simple circuit, using Ohm’s law.5.4 Resistance is affected by external factors. (e.g., temperature of conductor, length of conductor, cross-sectional area of conductor and material of the conductor).5.5 Compare and contrast alternating current (AC) and direct current (DC), and give examples of each.

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Four Parts to an Electrical Circuit

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Power Source Provide the force (EMF) to cause electrons to move. A battery, Generator, Photovoltaic Cells, Thermocouples Conductor Provides a path for the electrons to flow through the circuit. Copper is formed into wires, bars or channels.

Load The part of the circuit that changes the energy of moving electrons into some other useful form of energy. Lights, Motors, Heating elements are examples.

Control Regulates the flow of electrons in a circuit. Switches, potentiometers, thermostats, transistors are just some examples.

Schematic Diagrams

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Battery Open Switch (Off Position)

Closed Switch (On Position)

Lamp(incandescent)

AC Generator Ground i.e. Earth

Resistor

A standard way to represent electrical components using graphic symbols.

Potentiometer

Draw a schematic for a flashlight.

Schematic Diagrams

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Diode Capacitor Transformer Fuse

LEDLight Emitting Diode

Circuit Breaker

Outlet - GFCIGround Fault Circuit Interrupter

A standard way to represent electrical components using graphic symbols.

Relay SwitchSolenoidUse on Doorbell

GFCI

In a blue print of a house a GFCI is represented with a schematic like the one on the left

Parts of the AtomAn atom has three parts.

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Proton

Electron

Neutron

Is positively charged and located in the nucleus

Has no charge and is located in the nucleusIs negatively charged and is located in the electron cloud and orbits the nucleus.

There are the same number of protons (positive charge) as electrons (negative charge) in a balanced atom.

Creating Free Electrons and Positive Ions When two electrons with like charges get

close they repel one another.

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A Free Electron is formed and will randomly drift in the material.

The atom that is missing an electron is now a Positive Ion

Insulators and Conductors

Conductors are noted for having many free electrons.

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Insulators will have few free electrons as the atoms in these materials have a strong attraction between the electrons and protons

Metals such as copper, aluminum, gold have many free electrons and are used in many electrical applications.

Materials such as rubber, glass, ceramics, and most plastics.

Measuring DevicesVoltmeter- Measures volts or electrical

pressure

Ohm Meter- measures resistance to electron flow

Ammeter – measures current or the speed at which electrons flow.

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Series CircuitsProvide only one path for electrons to flow.

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When a circuit is closed the electrons pass through the conductor to each of the loads and back to the power source.

If one light bulb goes out……. they all go out because the path is open.

Electrons flow from negative to positive. The negative charged electrons are repelled from the negative terminal and attracted to the positive terminal.

Parallel CircuitsA circuit in which the loads are connect on

different branches.

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If one light bulb goes out …...

there is still a path for the electrons to flow through the circuitso none of the others will go out.

I’m a branch

Me Too!

Me Too!

Me Too!

Branches distribute the electricity down different paths.

Combinations of series and parallel circuitsWhen a circuit is wired in series/parallel only parts

of a circuit may be effected when a light fails.

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L1L2

L3

L4

L5

If lamp L3 burns out, which lamps will remain on and which will go out?

Only lamp L2 and L3 will be out the rest will remain on.

L1L2

L3

L4

L5If lamp L1 burns out, which lamps will remain on and which will go out?

If lamp L1 burns out all the other lamps, L2, L3, L4, and L5 will also go out because the path of the electrons has been open.

Houses are wire in a series/parallel with several branches with multiple outlets, lights ceiling fans on each branch.

Combinations of series and parallel circuitsMost circuits in a house are series/parallel. Each branch is is in series with the circuit breaker. Each light or outlet is in parallel with other items on the branch. Even if one device stops working, the others will still work.

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Ohm’s LawV= VoltageI= AmperageR= Resistance

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Ohms Law - Putting the 3 togetherOhm’s Law is a basic law about electricity.

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It shows the mathematical relationship between Electromotive Force or Voltage (E or V) Current (I) and Resistance (R) Current = Voltage/Resistance

Voltage = Current x Resistance

Resistance = Voltage/Current

V

I x R

This simple memory device may be used. Place your fingerover the unknown quantityand the math equation will

be be displayedA battery supplies 6 volts and the resistance is 12 ohms. What is the current?

6volts/12 = .5amps

Current=Volts/Resistance

A current is 3 amps and a resistance is 40 What is the voltage?

Voltage = Current x Resistance

3amps x 40 = 120Volts

Ohm’s Law Practice

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V

I x R

1. A circuit has an applied voltage of 100 volts and a resistance of 1000. What is the current flowing in the circuit?

I=V/R I=.1

1st List

what

you know

and don’t k

now.

V = 100 v

I = ?

R = 1000Ω

2nd Show Form

ula

3rd Show M

ath

I = 100V/1000Ω

4th ste

p show an

swer

5th Lab

el Answ

er

Amps

Ohm’s Law Practice

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V

I x R

2. A circuit has an applied voltage of 3 volts and a current flow of .5amps. What is the resistance required?

3. A circuit has an a current flow of 15amps with an appliance that has 8 of resistance. What is the applied voltage?

R=V/I

V= I x R V=120 volts

R=3v/0.5amps R= 6 Ω

V = 3 v

I = 0.5 amps

R = ?

V = 15 amps x 8 ΩV = ?

I = 15 amps

R = 8 Ω

DC Direct Current Current that is produced in a circuit by a steady

voltage source. Direct current is when electrons flow in one direction in a circuit only.

http://www.walter-fendt.de/ph14e/electricmotor.htm

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In direct current the voltage will go to maximum or PEAK (almost) instantly so on a graph it looks like this.

Vol

ts

Time0

Electrons flow from – to +

1 sec

AC Alternating CurrentCurrent that is produced by a voltage source that

changes polarity, or alternates, with time.

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In alternating current the voltage goes to PEAK positively then reverses to zero, the current then goes to PEAK in the negative.

Vol

ts

Time

0

When the electrons have gone once in each direction makes cycle and is represented with a sine wave as seen in the graph.

http://www.walter-fendt.de/ph14e/generator_e.htm Draw this graph on your paperDraw this graph on your paper

Electrical PowerThe rate at which electrical energy is delivered is

POWER. Power is also the rate at which an electrical circuit does the work to convert the energy of moving electrons into some other form of energy.

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The unit of measure for Power is the watt.

The watt is based on on the unit of work, joules per second.

100 watts light bulb uses 100 watts in one hour or 100 watt-hours.If the 100 watts light bulb uses 100 watts in one hour after ten hours the bulb has used 1000 watt-hours or 1 Kilowatt-hour.

The letter symbol for Power is P.

The Power Formula

We can calculate the power used by an appliance or item. Power is equal to the Electromotive Force (voltage) multiplied by the current.

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The formula is P = E x I

P

E x I

Using the same technique as the Ohm’s Law Memory device. To solve the problems at the Right.

An appliance is rated for 120 volts and draws 10 amps. What is the power used in one hour?

Or V

Formula: P = E x IMath: P = 120 volts x 10 amps

Answer: P = 1200 watts

Questions

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15. What is the power used of a circuit that has 120 volts and a current of 12 amps?

A. 12 wattsB. 12 voltsC. 1440 wattsD. 0.1 volts

The correct answers is _____C.

V = 30 v

I = 12 amps P=IE P= 12 amps x 120 volts P= 1440 watts

R = ?

P= ?

Questions

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16. If a speaker is rated for 8 Ω and it has 0.25 amps of current flowing to it then what is the Electromotive force at the speaker?

A. .5 wattsB. 1 wattsC. 2 wattsD. 16 watts

The correct answers is _____A.

V = ?

I = 0.25 amps V = IR V=0.25amps x 8 Ω V= 2 volts

R = 8 Ω

P= ?

P= IE P= 0.25 amps x 2 volts P= 0.5 watts

Electrical Safety

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Fuses have an internal wire that burns out if a current is too great.

House Fuse Car fuses In-line fuse Holder

and fuse

Electrical Safety

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Circuit breakers which will shut off the circuit if the current flows to much.

Electrical Panel

A relay Switch Transformer

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One circuit is used to control a second circuit. When Magnet coil is turned on it will attract the steel plate and move the switch closer turning on that circuit.

The primary coil in a Transformer produces a magnetic field that will influence the electrons in the second coil and current will flow. Used to step-up or step down voltage.

End of show for 2011

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Potential Difference or VoltagePotential difference is electrical potential or the difference in voltage between two points.

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1000 gallons

Just as in this example there is the potential to move 1000 Gallons of water from the upper tank to the lower tank.

A battery is rated by the number of volts it has or the potential difference it has between the positive and negative terminals at full charge. Potential Difference is measured in Volts

Anytime there is a difference in voltage between two objects (terminals) there is Potential Difference.

Potential Difference letter symbol is either V or sometimes E

The Law of Charges

Like charges

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MasterCard

Visa

American Express

Discover

Unlike charges

Repel Repel

AttractAttract

It should be noted that an area of influence (an electrical field) exists around each charge. Objects do not have to touch to repel or attract.

Electromotive ForceElectromotive force is the amount of push or

force that is in the wires pushing the electrons.

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Electromotive Force or EMF unit of measure is the Volts

Electromotive force would be equal to the pounds per square inch (PSI) that is the force of the water going through the pipe.

60 pounds per square inch

Electromotive force only exists when electricity is flowing.Electromotive force Letter symbol is either V or sometimes E

Electrical CurrentCurrent is the number of electrons to pass at one point in one second. It is the flow of electrons.

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Current would be like the number of gallons per minute are passing a point in the pipe.

Gallons per Minute

Current unit of measure is the Amperes or Amps. Currents Letter symbol is an I

ResistanceResistance is opposition to current flow.

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Resistance is the friction from the valve and the sides of the pipe.

The valve and pipe walls restricts the flow of water

The length of the conductor (wire) will have an effect on the current. The shortest extension cord should be used when using machines.

Resistance unit of measure is the Ohm or the omega symbol . The letter symbol is an R

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Series CircuitsOnly One Path

Here there are two light bulbs in series.

What is missing?

Power Source

Conductor

Load

Control – Control is by disconnecting a terminal anywhere in the circuit or remove a lamp.

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Parallel Circuits

A parallel circuit has more than one path each charge can follow.

Disconnecting a lamp terminal or removing a lamp would only stop one of the two lamps.

Electrical Safety

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Correct wiring is not enough to prevent electrical accidents. Most household circuits usually have an average voltage of 120 volts. Each device that is turned on increases the current. If the current exceeds the circuit’s safety limit, the wire may overheat.

Questions

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17. If one light on a string of holiday lights burns out and the rest do not the string is wired?

A. In seriesB. In parallelC. With a fuse.D. In combination.

The correct answer is _____B.

Questions

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18. Current that flows in one direction? A. Is AC and supplied by a battery

B. Is AC and is supplied by a generatorC. Is DC and is supplied by a generatorD. Is DC and supplied by a battery.

The correct answer is _____D.

Questions

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19. A house is typically wired in? A. Series

B. ParallelC. Series/ParallelD. The dark

The correct answer is _____C.

Questions

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20. AC current that has 60 hertz is typical in USA. This means that?

A. The voltage is at a peak usable 60 volts.B. The cycles per second are at 60 times a secondC. The watts will never exceed 60 wattsD. The amperes going into a residential home is 60

amps

The correct answer is _____B.

End of slide show

Current

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Electrical Current and Magnetic fields

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Electromagnetic induction

How generators work

Electromagnetic fields around a live wire

Compass influenced by current

Electromagnets and Solenoids

How speakers work

How electromagnets work