II. Important Circuit Concepts
Conservation of charge and
energy for electric
current
1) Kirchhoff's 1st Law
Total
current arriving
at a point in a circuit
=
Total current leaving
point.
(Conservation of Charge)
“Amps In = Amps Out”
Ex 1)
Amps In = Amps Out
| 5 Amps | = | 3 Amps + x |
X = 2 amps
Remember
“Amps In = Amps Out”
Ex 2) Current in bottom branch?
Amps In = Amps Out
| 2 Amps + X | = | 12 Amps |
X = 10 amps
Ex 3)
Amps In = Amps Out
| 22 Amps | = | x Amps + 6 Amps |
X = 16 amps
Amps In = Amps Out
5 A + x = 15 A
x = 10 A
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 you gain going down a ski slope (KE, Work against friction and snow)
Applied Voltage
( - )
Voltage Drop
( + )
0 = 12 V + -2 V + x + -6 V
0 = 12 V + -8 V + x
0= 4 V + x
x = - 4 volts
VT = V1 + V2 + ....