2. • First Capacitors
– Ewald Georg von Kleist (German)
A Little History
• 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. Capacitor
 2 conductors charged equal &
opposite separated by an insulator
+ – • 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
E battery is disconnected
• Battery pulls e’s from the + plate
and deposits them on the – plate.
Insulator blocks them from jumping
+ --
Battery back over.

5. 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?
+ e
--

6. 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?
+ -
+ -
+ -
+ -
+ -
+ -
+ -
+ -
+ -
+ e-
-

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

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

10. • Capacitance
Rating Capacitors
– Also determined by the
construction of the capacitors
• Area of plates (A)
• Distance between plates (d)
• Type of insulator between plates
(ε r - dielectric constant)
– Plastic, glass, ceramic, paper
εo εrA
C=
d

11. • Prevent information loss
Where ARE THEY?!
– 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