Chapter 20  "Electric Circuits"
I
=
q
t
I = current (amperes)
q = charge (coulombs)
t = time (seconds)
Ohm’s Law
V
=
IR
V = voltage (volts)
I = current (amperes)
R = resistance (ohms)
Resistance and Resistivity
R
=
ρ
L
A
R = resistance (ohms)
ρ
= resistivity (ohmm)
L = length (m)
A = crosssectional area (m
2
)
ρ
=
ρ
o
1
+
α
(
T

T
o
)
[
]
ρ
= resistivity at T (ohmm)
ρ
ο
= resistivity at T
o
(ohmm)
α
= temperature coefficient of resistivity (C
o
)
1
T = temperature (
o
C)
T
o
= temperature (
o
C)
R
=
R
o
1
+
α
(
T

T
o
)
[
]
R = resistance at T (ohmm)
R
ο
= resistance at T
o
(ohmm)
α
= temperature coefficient of resistivity (C
o
)
1
T = temperature (
o
C)
T
o
= temperature (
o
C)
Power
P
=
IV
=
I
2
R
=
V
2
R
P = power (watts)
I = current (amperes)
V = voltage (volts)
R = resistance (ohms)
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Alternating Current
V
=
V
o
sin2
π
ft
I
=
I
o
sin2
π
ft
V = voltage (volts)
V
o
= peak voltage (volts)
f
= frequency (Hz)
t
= time (seconds)
I = current (amperes)
I
o
= peak current (amps)
(Note:
2
π
ft
will be in radians.)
P
=
I
o
V
o
sin
2
2
π
ft
P = Power (watts)
P
=
1
2
I
o
V
o
_
P = Average Power (watts)
I
RMS
=
I
o
2
I
RMS
= Root Mean Square Current (amps)
V
RMS
=
V
o
2
V
RMS
= Root Mean Square Voltage (volts)
P
=
I
RMS
V
RMS
=
I
2
RMS
R
=
V
2
RMS
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 Spring '08
 Sharp
 Charge, Current, RC Circuits, Resistance, Resistor, Inductor, Electrical resistance, Series and parallel circuits

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