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TEST REVIEW ELECTRONS

• Electricity begins with Electrons.

ATOMS• Electron cloud surrounds an

atom’s nucleus• Nucleus is made of

• Electrons – negative charge• Protons – positive charge• Neutrons – zero charge (neutral)

Protons and Neutrons

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LOAD

• Power Source – with positive and negative terminals.

• Conductor – the path the electrons travel along.

• Load – this is what the electricity powers (e.g. motor, light bulb)

REVIEW CIRCUITS

• The paths that electrons travel are called circuits.• Circuits must consist of three things:

ELECTRONS move from negative ( - )

terminal to positive ( + )

terminal

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REVIEW CONDUCTORS

• Conduct – from Latin for “leading, guiding.” • A conductor is any material that allows electrons

to easily flow.• Remember the atom:

– Conductors’ electrons are not tightly bound to the atom.– Conductors have free electrons.

• Which material has free electrons, Wood or Metal?

• Metals conduct electricity easily.

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• Insulate – from Latin for “separate, divided.”

• An insulator is any material that impedes the flow of electrons.

• Remember the atom:– Insulators’ electrons are tightly bound to the atom. – Because the electrons don’t move, insulators cannot

conduct electricity very well, if at all.

• Which material has bound electrons, Wood or Metal?

• Wood does not have free electrons.

Review INSULATORS

CottonBound ElectronsGoldWoodPlasticSilverAluminumAirCopperFree-electrons

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INSULATORCotton

Wood

Plastic

Air

BOUND ELECTRONS

CONDUCTORCopper

Gold

Silver

Aluminum

FREE ELECTRONS

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Review Joule’s Law

• James Joule (1818 – 1889) – showed that heat and electrical energy are interchangeable.

• Joule’s Law:

Power = Voltage x Current

P = V I

Watts = Volts x Amperes

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• George Ohm (1789 – 1854) – a high school and university mathematics instructor

• Discovered ~1827• Voltage = Current x Resistance

V = I R

What are the units of this formula?

Volts = Amperes x Ohms

Review Ohm’s Law

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LOAD

NEGATIVEPOSITIVE

INSULATORS

CONDUCTORS

TERMINOLOGY

• Current (I) – the motion of electrons from one atom to the next in a material. – In our circuit, electrons flow from ___________ terminal

to the ___________terminal.– This motion of electrons through our conductor (wire) is

considered current (like water through a pipe).

• Materials that resist current are called ___________.

• Materials that provide a path for current are called ___________.

• Current is measured in AMPERES (Amps)

• Voltage (V) – the electric potential between two points of opposite charge.

• Voltage is the potential energy of the electrical power source.

• Voltage is measured in Volts (V).

Review TERMINOLOGY

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1. What is a schematic?

2. Which of the following is a schematic?

Review Electric Schematics

A schematic is a diagram that represents the elements of a system without using realistic pictures

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1. What does the following schematic symbol represent?

2. What does the following schematic symbol represent?

3. How many volts are typical in a residential electrical outlet?

4. What do graphs of DC and AC power sources look like? Why?

Review March 04, 2010

DRILL

DC Power Supply

AC Power Supply

120 volts

1) Write the given information:V = 144 Volts

P = 20,000 Watts I = ?

2) Sketch a schematic diagram of the circuit:

Start with power sourceAdd conductorsAdd load Add current

Review Problems – Joule’s Law

V = 144V

I = ?

-

+P = 20,000 W

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1) Write the given information:

V = 144 VoltsP = 20,000 Watts

I = ?

3) Rearrange, Substitute, and Solve

Review Problems – Joule’s Law

V = 5V

I = .7A

-

+R = ?

2) Sketch a schematic diagram of the circuit:

P = V x I

I = 20,000W / 144V

R = 138.9 A

I = P / V

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• Resistors in series are added:

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Review Resistance Calculations

R1 R2 R3

R = R1 + R2 + R3

T

Total Resistance:

• Resistors in parallel: add their reciprocals

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Review Resistance Calculations

R1 R2 R3

R R1 + R2 + R3T

Total Resistance:

1 1 1 1=

What is a schematic?

How would a schematic which includes an electric

motor look?

Review ELECTRIC MOTORS

A schematic is a diagram that represents the elements of a system without using realistic pictures.

V = 9V

I

Motor

Switch = Commutator

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• Now that you know what switches look like in electrical schematics, draw an electrical schematic for a lamp plugged into a wall outlet.

• Remember that AC power supplies look like in electrical schematics.

Review ELECTRIC MOTORS

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Review ELECTRIC MOTORS

120 VLamp

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• Resistance (R) –a measure of the degree to which an object opposes an electric current through it .

• Resisting an electric current often generates heat.– This is the principle behind how light bulbs work.

• Resistance is measured in Ohms (W – the Greek letter Omega)

Review TERMINOLOGY

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• Michael Faraday (1791-1867)

– London, England.

– Physicist and Chemist

• First person to successfully create an electric motor.

• Discovered that electric currents create a magnetic field, and vice versa.

Review Electric Motors

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• Electric motors are used everyday in many ways.• A motor’s purpose is to turn electrical energy into

mechanical energy.

Motors work on simple principles of magnetism:• Opposite poles _____________• Like poles _____________

Review ELECTRIC MOTORS

N SN S

ATTRACT

REPEL

NS

• If voltage is constantly 1.5 V, what does its graph over time look like?

Review Direct Current

Time (seconds)

Volt

ag

e (

volt

s)

0 2 4 6 8 10 12 14

1

2

3

1.5 V

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• If voltage is alternating 120 V to -120 V, what does its graph over time look like?

Review Alternating Current

Time (seconds)

Volt

ag

e (

volt

s)

0 2 4 6 8 10 12 14

-1

20

0

1

20

+/-120 V

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• Electricity can be used in a thousand different ways. For example: – Electric motors turn electricity into motion. – Light bulbs, fluorescent lamps and LEDs turn

electricity into light. – Computers turn electricity into information. – Telephones turn electricity into communication. – TVs turn electricity into moving pictures. – Speakers turn electricity into sound waves. – Stun guns turn electricity into pain. – Toasters, hair dryers and space heaters turn

electricity into heat. – Radios turn electricity into electromagnetic waves that

can travel millions of miles. – X-ray machines turn electricity into X-rays.

Review Electrical Technology

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1. An electric motor converts _________ energy into __________ energy.

2. List 4 household objects that use electric motors.

Review March 2, 2010

DRILL

ELECTRICAL

MECHANICAL

Fans Pumps Garbage disposer

Refrigerators Printers Microwave trays

Washing machines DVD players

Vacuums VCRs

ALMOST EVERY MECHANICAL MOVEMENT IN YOUR HOUSE

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Complete problem #5 on your worksheet

Review Problems – Joule’s Law

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5. A Lexus RX 100h hybrid has a 144 Volt battery system in its trunk. The electric motor that the batteries power can generate 20,000 Watts of power. Sketch a schematic diagram of this circuit. What is the current traveling through this high voltage circuit?

1) Write the given information:V = 144 volts

P = 20,000 watts I = ?

Review Problems – Joule’s Law

A schematic is a diagram that represents the elements of a system without using realistic pictures

1) Write the given information:V = 144 Volts

P = 20,000 Watts I = ?

2) Sketch a schematic diagram of the circuit:

Start with power sourceAdd conductorsAdd load Add current

ReviewProblems – Joule’s Law

V = 144V

I = ?

-

+P = 20,000 W

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1) Write the given information:

V = 144 VoltsP = 20,000 Watts

I = ?

3) Rearrange, Substitute, and Solve

Review Problems – Joule’s Law

V = 5V

I = .7A

-

+R = ?

2) Sketch a schematic diagram of the circuit:

P = V x I

I = 20,000W / 144V

R = 138.9 A

I = P / V

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• STUDY FOR TEST TOMORROW

• HAND IN REVIEW BEFORE TEST