Physics 2102
Exam II Study Guide
Current (i):
the net flow of charge; there must be a potential difference (V) to create a
current; measured in amperes [A].
=
i qt
Think of current (i) as positive charge carriers flowing through a wire. There must
be a complete path for current (i) to flow.
Conservation of Charge
=
=
+
iin iout
i1 i2 i3
Current Density (J):
describes current flowing across a crosssectional area of a
conductor; points in the direction of the flow of the current (i); measured in
[
]
Am2
=
i J∙dA
for constant J:
=
i JA
Resistance (R):
depends on the specific object in question; measured in ohms
.
Ω
=
R Vi
Resistivity (
ρ
):
depends on the material in question at a molecular level; measured in
ohm meters [
Ωm
].
=
ρ EJ
Conductivity (
σ
):
measured in inverse ohm meters
1Ωm
.
=
=
σ 1ρ JE
Loop Rule:
=
ΔV 0
around any closed loop in a circuit.
Junction Rule:
=
iin iout
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Across a Battery:
 to + ; V increases (+
E
)
+ to  ; V decreases (
E
)
Across a Resistor:
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 Spring '10
 DOWLING
 Charge, Current, Magnetic Force, Magnetic Field

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