A capacitor is a device that stores electrical potential energy by building up a difference in...
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Transcript of A capacitor is a device that stores electrical potential energy by building up a difference in...
A capacitor is a device that stores electrical potential energy by building up a difference in charge on two pieces of metal.
Capacitance is the ratio of net charge on each plate to the potential difference between the
plates. C = Q/ΔV
(or Q = VC)
The unit is the farad (F) , which is one coulomb per volt (C/V). A typical capacitor ranges from microfarads to picofarads.
F to pF1 F = 10-6 F1 pF = 10-12 F
Capacitance for a parallel plate capacitor is calculated from:C = ε0 A/dε0 is the permittivity of a vacuumA is the area of the platesd is the distance between the plates
The permittivity depends on the material between the plates. For a vacuum (or air), the value is 8.85 x 10-12 C2/N•m2. Permittivity is greater for other materials.
The material between the plates is an insulator and is called a dielectric. The presence of a dielectric increases the capacitance.
The molecules of a dielectric align themselves with the electric field, negative end toward the positive plate, and vice-versa.
The dielectric effectively reduces the charge at each plate, so the plate can store more charge for a given voltage. More charge means more capacitance for same voltage. (Q = VC)
C = ε0 A/d
As the equation indicates, the larger the plates of a capacitor, the higher the capacitance; and the further apart the plates are, the lower the capacitance.
Once a capacitor is charged, the source can be removed and the capacitor will retain the charge. If the two plates are connected by a conducting material, the capacitor will rapidly discharge. This discharge continues until the potential is zero.
Devices that use capacitors include: camera flash devices, computer keyboards, defibrillators, tasers and automobile blinkers.
A charged capacitor stores electrical potential energy. The amount is given by the following equation: PEelectric = ½QΔV
A 3.0 F capacitor is connected to a 12 V battery. What is the magnitude of the charge on each plate of the capacitor, and how much electrical potential energy is stored in the capacitor?