1. ELECTRICAL SKILLS CAPACITORS

2. FUNCTION OF A CAPACITOR Capacitors are used in electrical circuits to store electrical charges

3. CAPACITORS CONSTRUCTION A capacitor is made of two plates of a conductive material separated by an insulating material.

5. CAPACITORS TYPES Capacitors are classified according to the insulator material they use in between the plates of each capacitor. They are Air capacitors Plastic capacitors Mica capactors Ceramic capactors Elecrolyte capacitors

6. CAPACITY OF A CAPACITOR The capacitor is defined by its capacity C Capacity (C) is defined as the ability of acapacitor to store electrical charges (Q) -After the two plates are put under Electrical Voltage (V) C= Q / V C- Capacity. Q- Charge (Coulombs) V- Voltage (Volt)

7. CAPACITORS UNIT Capacitors are measured in Farads (F) Its smaller units are Microfarad (µF) Picofarad (pF)

8. PARAMETERS OF C C Depends on three factors - Plate area in square metre C increase with Area (A) - Distance between the plates (d) C decreases with distance (d) - Insulation constant of the insulator’s material (K)

9. C= ε A/d ε = ε 0 K ε 0= 8.85x 10 -12 C 2 Nm Dielectric constant (K) of different material Air – 1 Paraffin – 2.2 Paper – 3-7 Glass – 4-7 Mica – 7 Rubber – 2.8 Water - 80

10. CAPACITORS AS CIRCUIT ELEMENTS Capacitors can withstand a maximum voltage (V m ) Capacitors have different capacities C Hence Capacitors are chosen in an electrical circuit according to - Voltage V m (Volts) - Capacity C (Farads)

11. Capacitor in AC circuits Capacitor has a small Ohmic resistance Capacitor has a Reactance called X c (Ω) - X c = 1/ωc = 1/2¶ fc (f- frequency in Hz) In Dc f=0 then X c =infinity, no current can flow Thus Capacitor is used to stop DC currnts When f is big X c is small, Thus capacitor is used to pass the AC currents - If c is sufficiently large, X c is so small Thus capacitor can be used as an earth for AC currents in a DC circuits.

12. APPLICATIONS OF A CAPACITOR Voltage smoothing in a rectifier / charger Flash light in cameras- Electrolyte capacitors Tuning circuits in a radio receiver Air gap variable capacitors Pulse shaping in electronic circuits-Reular capacitors Integrator and differentiator circuits

13. ENERGY STORED IN A CAPACITOR The energy stored in a capacitor is given by E= ½ CV 2 Joules E- Energy C- Capacity V- Voltage

14. Problems Calculate C and Q for a capacitor with the following parameters Plate area 20cm x 3cm Air gap – 1mm Voltage – 12V

15. A 12V battery is connected to a 20µF capacitor which uses a paper dielecteic. How much energy can be stored in the capacitor?