1. Electrical Energy and Capacitance

2. Capacitors and Charge Storage
Capacitor – acts as a storehouse of charge and energy
Typically consists of two metal plates separated by a small distance
Called a parallel plate capacitor
When connected to a battery, charge is transferred from one plate to another until the potential difference of the capacitor is equal to the potential difference of the battery
The two plates will have equal and opposite charges

3. Capacitors and Charge Storage

4. Capacitors and Charge Storage
Capacitance – the ability of a conductor to store energy in the form of electrically separated charges
Ratio of charge to potential difference
Measured in farads (F)
Equivalent to a coulomb/volt (C/V)
Named in honor of Michael Faraday who contributed greatly to our knowledge of electromagnetism
Capacitors typically range from microfarads (10-6) to picofarads (10-12) in strength

5. Capacitors and Charge Storage
Capacitance = (magnitude of charge) / (potential difference)
C=Q/ΔV
Capacitance for a parallel-plate capacitor in a vacuum
Capacitance = (permittivity of a vacuum) * (area of one of the plates) / (distance between the plates)

6. Capacitors and Charge Storage
C=ε0 * A / d
ε (lowercase sigma) represents permittivity of a medium
The subscript 0 means that the medium is a vacuum
Permittivity has a value of 8.85*10-12C2/N*m2
Capacitance decreases with increasing distance
Capacitance increases with increasing size of the capacitor
Earth is so massive it is a excellent capacitor
Used for grounding
Can take a lot of charge without changing electric potential

7. Capacitors and Charge Storage
The material between the plates can change the capacitance
By inserting an insulating material called a dielectric (such as air, rubber, glass, or waxed paper) between the plates, the capacitance increases
Surface charges build up on the dielectric and reduce the charge on the plates
More charge can be stored
Charge is rapidly released when discharged by a capacitor
Discharged by connecting the plates with a conductor

8. Capacitors and Charge Storage

9. Energy and Capacitors
Electrical potential energy stored in a charged capacitor
Electric potential energy = ½ * (charge on one plate) * (final potential difference)
PEelectric = ½QΔV
The greater the charge on the plates, the more work and therefore energy that is needed to move charges between the plates
Other forms of the equation
PEelectric = ½CΔV2
PEelectric = Q2 / 2C
Capacitors have a maximum energy and charge they can store
Exceeding this maximum causes electrical breakdowns

10. Energy and Capacitors