I. Capacitor - A charge storage device, usually two conductors separated by an insulator.

A. Capacitance - C = Q/V_{ab }
Units:[Coulomb/volt] = [farad]

Q = magnitude of charge on either plate

V_{ab } = potential
difference between the conductors

II. Parallel plate capacitor

A. For parallel plates, the electric field between the plates is constant and depends on the charge per unit area.

B. What is the expression for the capacitance
of a parallel plate capacitor?

III. Capacitor connections

A. Series

(1/C_{eq}) = 1/C_{1} + 1/C_{2}

1. What physical quantity do capacitors in series have
in common?

B. Parallel

C_{eq} = C_{1} + C_{2}

2. What do capacitors in parallel have in common?

V. Energy stored in a charged capacitor - Energy = (1/2)(Q^{2}/C)
= (1/2)CV^{2} = (1/2)QV

A. What is the *energy density* for a charged parallel plate
capacitor?

VI. Dielectrics (non-conducting materials) can be used to increase the capacitance of capacitors.

A. When inserted between the plates of a parallel plate capacitor,
they effectively reduce the E-field between the plates. If E_{0}
is the original field, then the new field is E and

E = E_{0}/*k*

where *k* is the dielectric constant.

B. The new capacitance is now: C = *k*C_{0}
, where *k* is greater than 1.

C. Can you explain this, using an argument based on how electric
fields affect atoms and molecules?