By: Griffin Thomas

Capacitor

A capacitor is an electrical device that stores energy. Most electrical devices have some capacitance either intentional or accidental

The energy is stored by maintaining a potential difference between two conductors.

The energy is stored in the electric field between the conductors

Any electrical device that creates electrical fields creates some capacitance

The geometry of the capacitor affects the amount of energy stored. Capacitors are rated by capacitance, C, which is the ability of a given capacitor to store charge.

A dielectric is a material that when used in a capacitor increases the efficiency of the capacitor

A capacitor is unlike a power supply (which also maintains an electrical potential between two points) in that it is limited by the fact that it can store only a finite amount of charge.

CapacitanceCapacitance is the ratio of the magnitude of the charge in a capacitor to the magnitude of the potential difference in the capacitor

Capacitance is always a positive quantity Capacitance is a measure of the ability of a device to store

charge and electrical potential energy.

Units of capacitance:

1 Farad is a huge amount of capacitance. Typical capacitors have values on the order of 10-12

(picofarads) to 10-6 (microfarads) Capacitance depends upon the geometric arrangement of the

conductors (plates)

The Parallel Plate Capacitor

If one ignores the fringing field then the field between the plates is uniform. The distance between the plates is d.

• The field lines are parallel• The field lines are perpendicular to each plate

For an electric field between two parallel plates then: • Vb −VA = −Ed

The minus sign indicates that plate B is at a lower potential than plate A,VB < VA. Parallel plate capacitors are essential in physics

Calculations of Capacitance

The charge density for each plate is E between conducting plates is The potential between the plates is

Note that capacitance for a parallel plate capacitor is proportional to area and inversely proportional to d.

Video

https://www.youtube.com/watch?v=CFzCDg9yp7Q

Example

After watching the video and learning more, Lets solve a problem together. Remember ( C = Q/V )

1). Determine the amount of charge stored on either plate of capacitor (4x10^-6F) when connected across a 12 volt battery. C = Capacitance Q = Charge V = Volts

Answer: Q = (48x10^-6C) Give yourselves a pat on the back

Dielectrics Definition: Having the property of transmitting electric force

without conduction; insulating. Dielectrics increase the maximum operating voltage of a capacitor.

(Capacitance) Dielectrics may increase the mechanical strength of a capacitor. Example:

After introduction of the dielectric material, the preexisting field polarizes the dielectric.

Polarization of the dielectric establishes a field within the dielectric that opposes the external field causing the capacitance to increase thus strengthening the system. Invisible bonds man. Learn about ‘em.

Example Now lets jump into a new segment of dielectrics. Lets

find the area of the conductive plates. This is the formula:

Tip: Absolute permeability (dielectric) (e) = 8.85x10^-12

1). If the plate separation for a capacitor is 2.0x10^-3 m, determine the area of the plates if the capacitance is exactly 1 F.

Answer: 2.3x10^8 m^2

Capacitors in Parallel and Series Parallel series are circuits that conduct

electricity from a power source. With capacitors involved they can get trickier.

I will explain this in the schematics. Does anybody know how to make this look

simpler?

Solution?

Example By getting rid of all three capacitors you can make the

same circuit by creating a single capacitor with the total amount of capacitance.

Now how do you calculate total capacitance with similar and non-similar values like so:

Here is the first equation equation: Note: this is only if there are 2 capacitors Now here is the equation if there are more than 3

capacitors in a series:

Example

Lets solve the total capacitance together.

Hint: There are 3 capacitors.

You did it guys! Hooray! You beat the capacitance and dielectrics crash course! Bravo!