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II. Circuit Concepts
Conservation of charge and energy for electric current
Gustav Robert Kirchhoff This image is in the public domain because its copyright has expired.
1) Kirchhoff's 1st Law
“Amps In = Amps Out”
Ex 1)
Amps In = Amps Out 5 Amps = 3 Amps + x
X = 2 amps
Remember
Ex 2) Current in bottom branch?
Amps In = Amps Out
Ex 3)
Amps In = Amps Out
Ex 4)
Amps In = Amps Out 5 A + x = 15 A
x = 10 A IN
2) Kirchhoff's 2nd Law  the algebraic sum of all the voltage drops and applied voltages around a circuit = 0 (conservation of energy)
Amount of PE gained
when you go up a ski slope = energy released
going down a ski slope (KE, Work against friction and snow)
Applied Voltage
( + )
0 = 12 V + 2 V + x + 6 V
0 = 12 V + 8 V + x
0 = 4 V + x
x =  4 volts
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