Download Electric Circuits

Electric Circuits
Current:
Current: I =
Δq
Δt
⇒ Current flows because a potential difference across a conductor creates an electric
field which exerts a force on free electrons in the circuit.
Conventional current: the “hypothetical” flow of positive charge (it is really electrons
flowing in opposite direction)
Electromotive force or emf: the maximum difference in electrical potential between the
terminals of a battery
Ohm’s Law:
Ohm’s law: R =
ΔV
= constant
I
Ohm’s law is more commonly stated as: V = IR or I =
V
R
Resistance and Resistivity:
Resistance of a wire is given by: R =
ρL
A
Resistivity depends upon temperature: ρ = ρ 0 [1 + α (T − T0 )]
Power:
Power:
P = IV
P = I 2R =
applies to any circuit element
2
V
R
applies only to resistors
Resistors in series:
Resistors in parallel:
Current is the same through each resistor
Voltage is the same across each resistor
Voltage is split among individual resistors
Current is split among the individual resistors
Req = R1 + R2 + R3 + ...
1
1
1
1
=
+
+
+ ...
Req R1 R2 R3