14.4 CONDUCTION, INSULATION AND PROTECTION P

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”

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.

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.

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).

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 times necessary, 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

READING A RESISTOR For a 4 Band Resistor THE 1 ST 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%

Decode resistors p 468 Resistors are coated with ceramic. They have colour coded bands to indicate resistance 1 st & 2 nd band first two digits of resistance 3 rd band Number of zeros to add after the first two numbers.

Reminder Example: =  1st 2nd 3rd Black0 Brown1 Red2 Orange3 Yellow4 Green5 Blue6 Violet7 Gray8 White9 1 st band is red = 1 st digit is 2 2 nd band is orange = 2 nd digit is 3 = 23 The 3 rd colour is yellow = 4 so we add 4 zeros