OHM’S LAW The rate of the flow of the current is equal to electromotive force divided by resistance. I = Intensity of Current = Amperes E = Electromotive Force = Volts R = Resistance = Ohms P = Power = Watts The three basic Ohm’s law formulas are: E I = ––– R E R = ––– I E=IxR Below is a chart containing the formulas related to Ohm’s law. To use the chart, from the center circle, select the value you need to find, I (Amps), R (Ohms), E (Volts) or P (Watts). Then select the formula containing the values you know from the corresponding chart quadrant. PxR E I M H PS P E R TS AT W P I AM PR P I S LT VO E ExI RxI O 2 RxI S 2 E R 2 E R P 2 I E P Example: An electric appliance is rated at 1200 Watts, and is connected to 120 Volts. How much current will it draw? Watts Amperes = ––––– Volts P I = –– E 1200 I = –––– = 10 A 120 What is the Resistance of the same appliance? Volts Ohms = ––––––– Amperes E R = –– I -1- 120 R = –––– = 12 Ω 10 OHM’S LAW OHM’S LAW In the preceding example, we know the following values: In the preceding example, we know the following values: I = amps = 10 R = ohms = 12Ω I = amps = 10 R = ohms = 12Ω E = volts = 120 P = watts = 1200 E = volts = 120 P = watts = 1200 We can now see how the twelve formulas in the Ohm’s Law chart We can now see how the twelve formulas in the Ohm’s Law chart can be applied. can be applied. WATTS AMPS = ––––––– OHMS I = P 1200 ––– = ––––– = R 12 WATTS AMPS = ––––––– VOLTS I = P 1200 ––– = ––––– = 10A E 120 VOLTS AMPS = ––––––– OHMS I = E 120 ––– = –––– R 12 VOLTS WATTS = –––––– OHMS P = E 120 14,400 ––– = –––– = –––––– = 1200W R 12 12 WATTS = VOLTS x AMPS P = E x I = 120 x 10 = 1200W 2 2 2 100 = 10A = 10A 2 2 WATTS = AMPS x OHMS P = I x R = 100 x 12 = 1200W VOLTS = WATTS x OHMS E = VOLTS = AMPS x OHMS E = I x R = 10 x 12 = 120V WATTS VOLTS = –––––– AMPS 2 PxR = 1200 x 12 = 14,400 = 120V P 1200 E = –– = –––– = 120V I 10 2 2 VOLTS OHMS = ––––––– WATTS E 120 14,400 R = –– = ––––– = –––––– = 12Ω P 1,200 1,200 WATTS OHMS = ––––––– AMPS2 P 1200 R = ––2 = ––––– = 12Ω I 100 VOLTS OHMS = ––––––– AMPS E 120 R = –– = ––––– = 12Ω I 10 -2-