Slide1 : CH. 34 ELECTRIC CURRENT
POTENTIAL DIFFERENCE CHARGE FLOWS WHEN THERE IS A DIFFERENCE IN VOLTAGE ACROSS THE ENDS OF A CONDUCTOR
ELECTRIC CURRENT IS SIMPLY THE FLOW OF ELECTRIC CHARGE OR ELECTRONS.
THESE ELECTRONS ARE CALLED CONDUCTION ELECTRONS.
Slide2 : ELECTRIC CURRENT IS MEASURED IN AMPERES.
5 AMPS = 5 COULOMBS OF CHARGE IN ONE SECOND OR ABOUT 31.25 BILLION BILLION ELECTRONS EACH SECOND.
THE NET CHARGE OF ANY WIRE IS ZERO BECAUSE JUST AS MANY ELECTRONS LEAVE THE WIRE THAT ENTER IT.
Slide3 : A VOLTAGE SOURCE PROVIDES A SUSTAINED POTENTIAL DIFFERENCE TO ALLOW ELECTRONS TO FLOW.
DRY CELLS, WET CELLS, AND GENERATORS ARE GOOD VOLTAGE SOURCES.
DRY CELLS AND WET CELLS ARE THE RESULT OF A CHEMICAL REACTION.
GENERATORS CONVERT MECHANICAL ENERGY TO ELECTRICAL ENERGY.
Slide4 : VOLTAGE – IS THE ELECTRIC POTENTIAL PER CHARGE MOVING BETWEEN TERMINALS.
THIS IS LIKE THE ELECTRIC PRESSURE PUSHING THE ELECTRONS.
THE ALTERNATING POTENTIAL DIFFERENCE BETWEEN TWO HOLES IN A PLUG IS ABOUT 120 VOLTS.
VOLTAGE DOES NOT MOVE, IT PUSHES THE ELECTRONS.
Slide5 : ELECTRIC RESISTANCE CAN SLOW DOWN THE FLOW OF ELECTRONS.
RESISTANCE DEPENDS ON THE CONDUCTIVITY OF THE WIRE, AND ALSO THE THICKNESS AND LENGTH OF THE WIRE.
THICK WIRES HAVE LESS RESISTANCE.
SHORT WIRES HAVE LESS RESISTANCE.
RESISTANCE IS MEASURED IN OHMS ()
Slide6 : OHM’S LAW:
CURRENT = VOLTAGE / RESISTANCE
I = V / R
OR
1 AMPERE = 1 VOLT / 1 OHM
RESISTORS ARE USED IN ELECTRICAL DEVICES TO CONTROL THE RESISTANCE.
Slide7 : RESISTANCE IN THE BODY CAN BE FROM ABOUT 100 OHMS IF YOU’RE SOAKED IN SALT WATER TO ABOUT 500,000 OHMS FOR DRY SKIN.
TOUCHING A 120 VOLT ELECTRIC CIRCUIT NORMALLY WOULD DO NO HARM BECAUSE OF HIGH RESISTANCE
IF YOU WERE STANDING IN WATER, THE RESISTANCE IS LOWERED SO THAT THE CURRENT TRAVELS THROUGH FASTER.
Slide8 : BIRDS STANDING ON AN ELECTRIC WIRE ARE NOT HARMED BECAUSE THERE IS NO POTENTIAL DIFFERENCE.
DIRECT CURRENT (DC) – IS WHEN THE CURRENT FLOWS IN ONLY ONE DIRECTION. EX: BATTERY
ALTERNATING CURRENT (AC) – THE CURRENT FLOWS IN ONE DIRECTION THEN THE OTHER. EX: OUTLETS
Slide9 : IN THE U.S. WE ALTERNATE THE ELECTRIC CURRENT AT ABOUT 60 CYCLES PER SECOND OR 60 HERTZ.
DIODES CAN BE USED TO CHANGE AC TO DC CURRENT.
DIODES ALLOW ONLY HALF THE ELECTRONS TO FLOW THROUGH SO THAT THEY ARE ALL FLOWING IN THE SAME DIRECTION.
Slide10 : AT ROOM TEMP. ELECTRONS HAVE A SPEED OF A FEW MILLION KILOMETERS PER HOUR.
THE ELECTRIC FIELD AROUND THE ELECTRONS MOVES AT NEARLY THE SPEED OF LIGHT.
INSIDE WIRE, THE ELECTRIC FIELD IS DIRECTED ALONG THE WIRE.
Slide11 : IN DC CURRENT THE ELECTRONS DRIFT ABOUT .01CM/S
IN AC CURRENT THE ELECTRONS MOVE A FRACTION OF A CM IN ONE DIRECTION THEN MOVE BACK THE SAME AMOUNT EQUALLING NO NET MOVEMENT.
ELECTRONS THEMSELVES DO NOT FLOW.
Slide12 : ELECTRONS ALREADY IN A MATERIAL VIBRATE CAUSING ENERGY TO FLOW BY THE ELECTRIC FIELD.
THEREFORE POWER PLANTS DO NOT SELL ELECTRONS, THEY SELL ENERGY AND YOU SUPPLY THE ELECTRONS.
Slide13 : ELECTRIC POWER IS THE RATE IN WHICH ELECTRICITY IS CHANGED TO MECHANICAL ENERGY, HEAT, OR LIGHT.
ELECTRIC POWER = CURRENT X VOLTAGE
OR
1 WATT = 1 AMP X 1 VOLT
P = I X V
Slide14 : A KILOWATT IS 1000 VOLTS.
A KILOWATT HOUR IS THE AMOUNT OF ENERGY CONSUMED IN ONE HOUR AT THE RATE OF 1 KILOWATT.