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Transcript
Capacitors (17.7-17.9)
Capacitors are elements used in circuits to
store electric charge (and energy) and to
block surges of electricity, protecting circuits
Caps typically consists of 2 conducting
plates placed near each other but not
touching.
 Sometimes they are wrapped into a
cylinder like a burrito or one of those
“healthy wraps”

Capacitors: what are they?

Capacitor is basically 2 places separated
by an air gap (the gap can be filled with a
dielectric to increase the capacitance)
Capacitor

They look like this
Capacitor

Circuit with capacitor, resistor, battery
Caps in circuits
When placed in a circuit and voltage
source, charges flow onto the plates.
 Q = CV = total charge on the capacitor
 C is called the Capacitance and its
measured in Farads.
 C depends on the geometry of the
Capacitor…C = ЄA/d where Є = a
constant , A is the area of the plate, and d
= distance between the plates.

Capacitors
A dielectric is a material which is placed
between the plates in a capacitor.
 A dielectric does not allow electric charge
to jump across the gap as easily as air, so
higher voltages can be used.
 Dielectrics also increase the Capacitance
of the capacitor.

Capacitors and Dielectrics
Dielectrics increase the capacitance by a
factor of K.
 K = dielectric constant = material
property
 C = KЄA/d
Mtl
K
Vacuum
1.0
Paper
3.7
Rubber
6.7
Waffle
9.3

Dielectrics (17.8)
Caps store energy
 E = ½ CV2 (V = Voltage, not velocity…duh)

Energy in a capacitor
Caps in Parallel have the same voltage and
you find the total charge Q on each plate
using Q = CV.
Capacitors in circuits (19.5)
Caps in parallel have the same
Voltage

Capacitors in Series: Each plate of the
caps in series has the same CHARGE = Q
Caps in Series
The rules for “combining capacitors” in a
circuit is just the opposite as the resistor
rules…..
Circuit
Voltage Charge
Cequiv
Parallel
Same
Adds Ceq=C1+C2
Series
Adds Same
I/Ceq= 1/C1 + 1/C2

Capacitors in series and parallel