14.4 CONDUCTION, INSULATION AND PROTECTION

P 464 - 468

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CONDUCTION: Energy transfer from one material to another

by direct contact.

Electrical energy transfers electrons

Conductors are materials that allow transfer to happen. Ex: copper, aluminum, silver and optical fibers. See youtube engineerguyvideo “how a laser works”

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Transition metals are good conductors of electricity and heat.

PRINTED CIRCUITS

ELECTRICAL CIRCUIT PRINTED ON A THIN RIGID BOARD

Printed circuits: Board = thin plastic sheet covered with

copper. A circuit is etched in. Extra copper is removed. Electric and electronic components are then

soldered on.

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MASS MANUFACTURING OF CIRCUIT BOARDS VIDEO Printed Circuit Board Video There are many devices that use circuit

boards: Cell phones, MP3 Players, DVD players, TV’s, Computers, and the list can go on….

INSULATION It’s electrical

function is: To PREVENT THE FLOW OF ELECTRIC

CURRENT

Prevent INJURY as well as SHORT CIRCUITS

CERAMIC & PLASTIC are good insulators that can be wrapped around a wire, or used to contain electric flow.

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PROTECTION FUSES & CIRCUIT BREAKERS are used to

protect circuits

These components stop the current flow in the event of a short circuit or power surge (overload).

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Fuses: Regulate the amount of amps that go through a circuit. Electrons will flow through the filament of a fuse when working

properly.

Filaments can be found in light bulbs, diodes etc. If the current intensity is to high the filament will either

melt, or break into two pieces. At this point the fuse will need to be replaced.

Filament

Breaker

• It is a protective device that can be reset as many timesnecessary, thus it is better than a fuse as a fuse needs to be replaced every time the filament breaks.

• Electrons flow through a bimetallic strip. If the current intensity gets to high, the strip heats up and bends.

• The bending of this strip makes the breaker shut off and snap over to the off position.

• When this happens you can go to your breaker panel and reset the breaker switch.

14.5 ELECTRICAL RESISTANCE

RESISTORS LIMIT THE FLOW OF ELECTRONS THROUGH AN ELECTRICAL CIRCUIT

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READING A RESISTORFor a 4 Band Resistor THE 1ST TWO BANDS TELL YOU THE FIRST TWO

DIGITS OF RESISTANCE ex. RED=2; BLUE=6

THE NEXT BAND TELLS YOU WHAT TO MULTIPLY THOSE NUMBERS BY ex. RED=100

LAST BAND IS TOLERANCE FACTOR EX. GOLD= ±5%

THEREFORE A RESISTOR WITH RED, BLUE, RED, GOLD WOULD HAVE RESISTANCE OF 2600 Ω ±5%

Review

Decode resistorsp 468

Resistors are coated with ceramic. They have colour coded bands to

indicate resistance

1st & 2nd band first two digits of resistance

3rd band Number of zeros to add after the first two numbers.

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Reminder

   

Example:

= 230 000 W

1st

2nd

3rd

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Gray 8

White 9

1st band is red = 1st digit is 2

2nd band is orange = 2nd digit is 3

= 23The 3rd colour is yellow = 4

so we add 4 zeros