Capacitors store electric charge and their capacitance is measured in Farads. The capacitance of a parallel plate capacitor depends on the surface area of the plates, the distance between them, and the dielectric material between the plates. Capacitors can be connected in parallel, in which case the total capacitance is the sum of individual capacitances, or in series, in which case the reciprocal of the total capacitance is the sum of the reciprocals of the individual capacitances. Energy is stored in a charged capacitor and can be calculated using the formula of one-half the capacitance times the voltage squared. Capacitors have various uses including in radios, switches, charge storage, power supplies, and ampl

1. PHYSICS
CAPACITORS
Short revision series

2. Capaitors
 2 conductors separated by an insulator
 Capacitance iss the ability of a conductor to
store charge. Measured in Farads F.
 C = Q  Q
p.d V V
Q = CV
V = Q/C

3.  Parrallel plate capacitor with an area A and
separated by distance d
 C = ε0 εr A
d
 Capacitors in parrallel
 C = C1 + C2
 Capacitors in series
 1/C = 1/C1 + 1/C2

4. Eg
 A parallel plate capacitor is charged to 200V
in a vacuum. It has an area of 100mm2 and
separated by 20mm space filled with mesh
of εr = 5. What is the capacitance?

5.  C = ε0 εr A
d
 = 8.85 x 10-12 x 5 x 100 x 10-3
20 x 10-3
= 2.21 x 10-10 F.

6. Energy stored in a charged capacitor
= average potential difference x charge
½ QV
V = Q/C
W = ½ QQ/C = ½ Q2/C
 Can still be expressed as
 ½ CV2
substituting Q = CV

7. Eg
 Consider a circuit with 3 capacitors of 4 μF
each in parallel with a potential of 50V
across the circuit. What is the capacitance?
What is the energy stored?

8.  C = C1 + C2 + C3
 = 12 μF
 Energy stored
= ½ CV2 = ½ x 12 x 10-6 x 502
= 15 x 10-3 J

9. Uses of capacitors
 Tuning in radio circuits
 Prevention of sparking in switches
 Charge storage
 Smoothening rectified current from dc power
supplies
 Blocking noise in ac amplifiers.

10. END