Capacitors

V = Ed E = V/d, with units of volts/meter A uniform electric field is an electric field in which the field strength does not vary. This gives a constant force on any charge that exists in the field. electric potential difference = work per unit charge = force x distance per unit charge = force per unit charge x distance = electric field strength x distance V = Ed E = V/d, with units of volts/meter

made of two conductors separated by an insulator Capacitor a device that stores charge made of two conductors separated by an insulator The amount of charge that a capacitor can store depends on: 1. area of conducting surface 2. distance between the conductors 3. type of insulating material link

Capacitance Q = CV C = Q/V the ratio of charge to potential difference The SI unit of capacitance is the Farad, F, named in honor of Michael Faraday. One Farad of capacitance means that one Coulomb of charge may be stored in the capacitor for each Volt of potential difference applied.

In other words, in a series circuit, capacitance adds as reciprocals, Capacitor Circuits Series 1. reciprocal of the total capacitance is the sum of the reciprocals of the separate capacitors 1/CT = 1/C1 + 1/C2 + 1/C3 + ... 2. charge is the same on each capacitor QT = Q1 = Q2 = Q3 = ... 3. total potential difference is the sum of each VT = V1 + V2 + V3 + ... In other words, in a series circuit, capacitance adds as reciprocals, charge stays the same, and voltage adds.

C, mF V, V Q, mC E = 12 V C1 12 C1 C3 C2 10 C3 15 CT = C2 VT = QT =

CT = 4.0 mF VT = 12 V QT = 48 mC E = 12 V C1 12 4.0 48 C1 C3 C2 10 4.8 15 3.2 48 CT = 4.0 mF C2 VT = 12 V QT = 48 mC

Parallel CT = C1 + C2 + C3 + ... QT = Q1 + Q2 + Q3 + ... 1. total capacitance is the sum of each separate capacitor CT = C1 + C2 + C3 + ... 2. total charge is the sum of the charges on each separate capacitor QT = Q1 + Q2 + Q3 + ... 3. potential difference is the same across each capacitor VT = V1 = V2 = V3 = ... In other words, in a parallel circuit, capacitance and charge add, but voltage stays the same.

C, mF V, V Q, mC E = 12 V C1 8 C2 10 C1 C3 4 C2 CT = C3 VT = QT =

CT = 22 mF VT = 12 V QT = 264 mC E = 12 V C1 8 12 96 C2 C1 10 12 120 48 C2 CT = 22 mF C3 VT = 12 V QT = 264 mC

Capacitors are often used in conjunction with resistors in simple circuits that are called RC Circuits. Click here and here to view computer simulations of this type circuit. Explore this link to learn more about capacitors.