1. For the things of this world cannot be made known without a knowledge of mathematics. - Roger Bacon -

2. ELECTRICAL EFFECTS ARE CAUSED BY ELECTRONS, BECAUSE ELECTRONS CAN MOVE MORE EASILIY THAN PROTONS. PROTONS ARE DIFFICULT TO REMOVE FROM AN ATOM, AS THEY ARE IN THE NUCLEUS. SINCE ELECTRONS ARE IN THE OUTER SHELLS, THEY CAN BE REMOVED. TO CREATE A CHARGE, WORK MUST BE DONE ON THE ELECTRONS TO SEPARATE THEM FROM THE ATOMS.

3. VOLTAGE DESCRIBES THE POTENTIAL ENERGY PER CHARGE AT A PARTICULAR LOCATION. VOLTAGE IS STORED POTENTIAL ENERGY OF ELECTRONS. e - e - e- e - e - e - e - + + + + + AB THE ELECTRICAL POTENTIALS (VOLTAGE) AT A AND B WILL BE DIFFERENT. THE POTENTIAL DIFFERENCE OR VOLTAGE DIFFERENCE WILL BE WHAT WE CALL VOLTAGE.

4. THINK OF VOLTAGE AS WHAT IS DRIVING THE FLOW OF ELECTRONS. SOMETIMES THE ANALOGY IS MADE TO A STREAM FLOWING DOWN A HILL. THE SLOPE OF THE HILL DETERMINES HOW FAST THE WATER FLOWS. THE VOLTAGE DETERMINES HOW HARD THE ELECTRONS ARE PUSHED. VOLTAGE IS MEASURED IN VOLTS.

5. THINK OF CURRENT AS THE FLOW RATE OF ELECTRONS. CURRENT CAN’T FLOW WITHOUT VOLTAGE. CURRENT IS MEASURED IN AMPERES OR AMPS, A. YOU NEED A COMPLETED CIRCUIT FOR CURRENT TO FLOW.

6. CURRENT IS MEASURED WITH AN AMMETER. THE AMMETER NEEDS TO BE PART OF THE CIRCUIT.

7. O.K., WE’VE TALKED ABOUT THE FORCE MOVING THE ELECTRONS (VOLTAGE) AND THE RATE OF FLOW OF ELECTRONS (CURRENT), NOW THERE IS A THIRD FACTOR AFFECTING ALL OF THIS – THE RESISTANCE TO FLOW OF ELECTRONS OR RESISTANCE. RESISTANCE DESCRIBES HOW EASILY AN OBJECT RESISTS CURRENT FLOW. SOME MATERIALS DO NOT GIVE UP THEIR ELECTRONS EASILY, SO THEY HAVE MORE RESISTANCE.

8. SO, RESISTANCE IS THE OPPOSITION TO FLOW OF ELECTRONS. SOME MATERIALS HAVE ELECTRONS VERY TIGHTLY BOUND, SO THEY WOULD HAVE HIGH RESISTANCE (NONMETALS). SOME MATERIALS HAVE ELECTRONS VERY LOSELY BOUND, SO THEY WOULD HAVE LOW RESISTANCE (METALS). RESISTANCE IS SORT OF LIKE FRICTION. IF THE RESISTANCE IS HIGH, SOME ELECTRICAL ENERGY WILL BE LOST AS HEAT, AND THE OBJECT WILL HEAT UP.

9. IN SOMETHING LIKE A LIGHT BULB FILAMENT OR AN ELECTRIC TOASTER FILAMENT, YOU WOULD WANT SOMETHING WITH HIGH RESISTANCE. THAT WAY, YOU COULD CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY AND IN TURN, INTO LIGHT ENERGY. IF VOLTAGE IS EXPRESSED IN VOLTS, AND CURRENT IS EXPERSSED IN AMPS, RESISTANCE WILL BE IN OHMS. I = V / R

10. THINK ABOUT THE ABOVE FORMULA AS FOLLOWS. I, THE RATE OF FLOW OF ELECTRONS OR CURRENT, INCREASES AS THE VOLTAGE INCREASES – THE BIGGER THE PUSH, THE GREATER THE FLOW. SO, I IS DIRECTLY PROPORTIONAL TO V. R IS THE RESISTANCE, SO, AS R INCREASES, I WILL DECREASE. I IS INVERSELY PROPORTIONAL TO R.

11. THE EQUATION, I = V / R, IS KNOWN AS OHM’S LAW. WE CAN USE IT IN THIS FORM TO CALCULATE THE CURRENT IN A CIRCUIT. EXAMPLE: IF A 1.5 V BATTERY IS CONNECTED TO A CIRCUIT THAT HAS A RESISTANCE OF 6 OHMS, WHAT IS THE CURRENT IN AMPS? V = I/R = 1.5V/6 ohms = 0.25 A WE CAN USE THIS FORMULA TO CALCULATE ANY ONE VARIABLE, KNOWING THE OTHER TWO.

12. POWER IS GIVEN BY THE FOLLOWING FORMULA: POWER = VOLTAGE X CURRENT P = V X I AND POWER IS IN WATTS WHAT WOULD BE THE POWER RATING OF AN 110 V CIRCUIT THAT HAS A CURRENT OF 5 AMPS? P = V X I = 110 X 5 = 550 WATTS AGAIN, IF YOU KNOW ANY 2 OF THE VARIABLES, YOU CAN CALCULATE THE 3 RD.

13. YOU HAVE A CALCULATOR THAT OPERTES AT 315 WATTS AND DRAWS 4.5 A CURRENT. AT WHAT VOLTAGE DOES IT OPERATE? P = V x I or V = P / I So, V = 315w / 4.5 A = 70 v

14. A MORE USEFUL FORM OF THE EQUATION MIGHT BE I = P/V YOUR HOUSE IS DIVIDED INTO A SERIES OF CIRCUITS, AND EACH ONE IS HOOKED TO A CIRCUIT BREAKER THAT IS RATED FOR A CERTAIN NUMBER OF AMPS. THE REASON FOR THIS IS THAT IF YOU PUT TOO MUCH CURRENT THROUGH A WIRE, IT HEATS UP. IF IT GETS TOO HOT, IT COULD MELT AND START A FIRE. THE CIRCUIT BREAKERS ARE THERE TO PREVENT THAT. MANY HOUSEHOLD CIRCUITS ARE RATED AT 20 AMPS.

15. YOU PURCHASE A WASHING MACHINE THAT IS RATED AT 750 WATTS. YOU WANT TO PLUG IT INTO AN 120 V CIRCUIT THAT IS RATED AT 15 AMPS. CAN YOU DO IT? I = P / V = 750/120 = 6.25A

16. YOUR ELECTRICAL UTILITY COMPANY CHARGES YOU BASED ON HOW MUCH ENERGY YOU USE. THIS CAN BE CALCULATED AS FOLLOWS: ELECTRICAL ENERGY = POWER X TIME E = P X T IF POWER IS IN WATTS AND TIME IS IN SECONDS, ENERGY WILL BE IN JOULES.

17. YOU LEAVE A 30 WATT CPF LIGHT BURNING FOR 1 HOUR, HOW MUCH ENERGY HAVE YOU USED? E = 30 X 60 X 60 = 108,000 J CURRENTLY, THE COST OF POWER IN NC FROM DUKE POWER IS $0.093587 PER KWH. HOW MUCH WOULD IT COST TO LEAVE A 100 WATT LIGHT BULB BURNING FOR 30 DAYS?

18. ENERGY = 100W X 30 days X 24 hours/day = 72000 w-hr = 72 kw-hr COST = 72 kw-hr x $0.093587 /kw-hr = $6.74