Capacitors A capacitor is a device that has the ability “capacity” to store electric charge and energy.

Capacitors In a circuit diagram a capacitor is represented by two parallel lines of equal length

Capacitors

Figure A Parallel-Plate Capacitor

Capacitors

A dielectric material is an insulator that increases the capacitance of a capacitor when placed between the plates. Each material has a dielectric constant  not to be confused with k.(p 665)

Figure The Effect of a Dielectric on the Electric Field of a Capacitor

Capacitors

Capacitors connected in parallel have an equivalent capacity equal to the sum of the individual capacities.

Capacitors The charge on individual capacitors will be equal to

Capacitors The total charge in the circuit will be equal to

Capacitors Capacitors connected in series have an equivalent capacity whose reciprocal is equal to the sum of the reciprocals of the capacities of the individual capacitors.

Capacitors

Capacitors connected in series all have the same charge Q

Figure Capacitors in Series

Capacitors Voltage drops across capacitors connected in a series

Capacitors Voltage drops across capacitors connected in a series

Capacitors Capacitors connected in parallel have an equivalent capacitance which is equal to the sum of the capacitances of the individual capacitors.

Figure Capacitors in Parallel

Capacitors

Charges on capacitors connected in parallel are calculated by multiplying the voltage drop by individual capacitances.

Capacitors

Figure Capacitors in Parallel

Example 21-8 Energy in Parallel

Figure Capacitors in Series

Active Example 21-3 Find the Equivalent Capacitance and the Stored Energy

Figure A Typical RC Circuit

Figure Charge Versus Time for an RC Circuit

Figure Current Versus Time in an RC Circuit

Example 21-9 Charging a Capacitor

Figure Discharging a Capacitor

Figure Problems and 21-55

Figure Problems and 21-87

Figure Problem 21-78

Capacitors Solve problems on pages 711 and 712.