Ohm’s Law

Electronic Resistance: Material’s resistance to the flow of electric current Thin wire 120V Thick wire HEAT LIGHT

Ohm’s Equation voltage Current = resistance directly inversely Current is ________ proportional to voltage Current is ________ proportional to resistance inversely

Equation: symbol/units V I = R Volts (V) Amperes (A) = Ohms (Ω)* * Ω = OMG

Practice #1 How much current will flow through a lamp that has a resistance of 60 Ω when 12V are impressed across it? voltage Current = resistance 12 V Current = = 0.200 amps 60 Ω

Practice #2 What is the resistance of an electric frying pan that draws 12 A when connected to a 120 V circuit? voltage Current = resistance 120 V 12 A = = 10.0 Ω R

Resistance in series 2 Ω V I = R 6 V 6 V I = 2 Ω Current = 3.00 amps

Multiple Resistance in series: ADD! 2 Ω V I = R 6 V 6 V I = 2 Ω + 2 Ω 2 Ω Current = 1.50 amps

Resistance in parallel: R equivalent = (R1R2) / (R1+R2) 2 Ω R = (2x2)/(2+2) = R = 4/4 = 1 Ω 1 Ω 2 Ω = V I = R 6 V I = 1 Ω Current = 6.00 A 6 V

Series and Parallel: R equivalent = R1R2 / R1+R2 4 Ω 2 Ω = 4 + 2 = 6 Ω parallel (6x6) /(6+6) = 6 Ω = 36/12 = 3 Ω V 6 V I I = = R 3 Ω 6 V Current = 2.00 A Add series Ω first

Series and Parallel: R equivalent = R1R2 / R1+R2 4 Ω 6 Ω top series 4 + 6 = 10 Ω inside parallel (10x10) / (10+10) = 10 Ω 100/20 = 5 Ω 5 Ω = inside series 5 + 5 = 10 Ω 10 Ω final parallel (10x10) / (10+10) = 100/20 = 5 Ω V 6 V I I = = 6 V R 5 Ω Current = 1.20 A Work from the inside out

More than two Parallel: Solve two at a time! = top series 4 + 8 = 12 Ω 4 Ω 8 Ω top two parallel (4x12) / (4+12) = 48/16 = 3 Ω 4Ω final parallel (10x3) / (10+3) = 10 Ω 30/13 = 2.31 Ω V 6 V I I = = R 2.31 Ω Current = 2.60 A 6 V

Parallel Then Series: Current = 2.00 A I Solve parallel first 2 Ω R = (2x2)/(2+2) = R = 4/4 = 1 Ω 2 Ω Series: 1 + 2 = 3 Ω 2 Ω 6 V I = 3 Ω Current = 2.00 A 6 V Solve parallel first

1/R equivalent = 1/R1 +1/R2 + … Alternate equation to calculate resistance.