This document discusses the history and operation of capacitors. It explains that capacitors store charge on two conductors separated by an insulator. The first capacitor was the Leyden Jar invented in 1745. Capacitance is defined as the ratio of stored charge to potential difference and depends on the area of the plates and distance between them. Capacitors are used to prevent information loss, store energy for high power applications like lasers, and in applications like cameras and keyboards that require short bursts of energy.

2. ALittleHistory• First Capacitors
–Ewald Georg von Kleist (German)
• 1745
–Pieter van Musschenbroek (Dutch)
• Leyden Jar
–Benjamin Franklin (American)
• Franklin Square
–Michael Faraday (English)
• Wanted to store unused electrons from
experiments
• Oil drums
• Unit of capacitance named after him

4. • Battery charges the plates until the
potential difference (voltage)
between them is equal to the voltage
of the battery
• These stay charged even after the
battery is disconnected
• Battery pulls e’s from the + plate
and deposits them on the – plate.
Insulator blocks them from jumping
back over.
Capacitor
 2 conductors charged equal &
opposite separated by an insulator
E
─+
–
–
–
–
+
+
+
+

5. + -e-
Just a few questions:
1) What is flowing through the wire?
2)What function does the battery have?
3)Is this animation an accurate depiction of the
behavior of the electrons in the circuit?

6. + -e-
-
-
-
-
-
-
-
-
-
+
+
+
+
+
+
+
+
+
Just a couple of questions:
1) Will the charges build up on the plates FOREVER?
2)When will the charges stop flowing?
3)Why don’t the charges jump from one plate to the other?

7. + -
-
-
-
-
-
-
-
-
-
+
+
+
+
+
+
+
+
+
Just one question:
1) What will happen to a light bulb if we include it in the
circuit?

9. RatingCapacitors
• Capacitance
– The ratio of stored charge to the electric
potential difference
Charge
(Coulombs - C)
Potential Difference
(Volts - V)
Capacitance
(Farads - F)Q
V
Area under
curve?
Q α V
Q = VCSlope?
1
2
1
2
A bh
QV
=
=
Q
V
=
Summary of Variables & Units
Q Charge C
V Voltage (Electric
Potential)
V
C Capacitance F
PEC Potential Energy J
E Electric Field N/C

10. RatingCapacitors
• Capacitance
–Also determined by the
construction of the capacitors
•Area of plates (A)
•Distance between plates (d)
•Type of insulator between plates
(εr - dielectric constant)
–Plastic, glass, ceramic, paper
C =
εo εr A
dC α
εr A
d

11. WhereARETHEY?!• Prevent information loss
– Supplies power while battery charges
• Car audio for amplifier
– Stores energy for demand
• Pulsed lasers
– High energy, short time lasers
• Weapon detonators
– nukes
• Flashes in cameras
– Listen to them whine
• Keyboards
– Changes distance between plates
• Fuel level detection in airplanes
– Changes properties of insulator (fuel)
• Defribulators
– Sends an instant discharge through the heart