Study Guide
There will likely be an exam question involving capacitors, inductors, or both.
Capacitors (sections 26.1, 26.2, and 26.4)
A capacitor is a circuit element that stores electric charge. This charge creates a potential difference across the capacitor:
U œ GZ
The constant is the capacitance . Capacitance is measured in farads, where F C V.
A typical capacitor consists of two parallel plates of conductive material. The two plates hold equal and opposite charges, and have a very large electric field between them. The capacitor stores energy in this electric field: energy œ
U #
#G
Problems: Chapter 26 # 1, 27
Inductors (sections 32.1 and 32.3)
An inductor is a circuit element that opposes changes in the flow of current. The potential difference across an inductor is proportional to the rate at which the current is changing:
Z œ P
.M
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The constant is the inductance . Inductance is measured in henries , where H œ " V s A.
A typical inductor is a solenoid , or coil of wire. When current flows through the solenoid, it produces a strong magnetic field along its length. The inductor stores energy in this magnetic field:
" energy œ M P
#
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Problems: Chapter 32 # 1, 27, 28
Answers: 28. (a) #!Þ!
W (b) #!Þ!
W (c) !
(d) #!Þ!
J

RC, RL, and LC Circuits (sections 28.4, 32.2, and 32.5)
An RC circuit has a resistor and a capacitor, plus possibly a battery. An RC circuit reaches a steady state exponentially, with time constant
7 œ VG
An RL circuit has a resistor and an inductor, plus possibly a battery. An RL circuit also reaches a steady state exponentially, with time constant
7 œ
P
V
Both of these circuits obey the general rule
E œ E /
>Î 7 where is any circuit variable that goes to zero . You must think about the nature of the circuit to determine what will go to zero.
An LC circuit has an inductor and a capacitor. An LC circuit oscillates, with angular frequency
= œ
"
È
PG
Since an LC circuit has no resistor or battery, energy in the circuit is conserved. This lets you use the formulas for the energy in a capacitor or inductor to determine information about the circuit.
RC Circuit Problem: Chapter 28 # 29
RL Circuit Problem: Chapter 32 # 13
LC Circuit Problem: Chapter 32 # 37