1. Capacitors

2. What is a capacitor? Electronic component Two conducting surfaces separated by an insulating material Stores charge Uses –Time delays –Filters –Tuned circuits

3. A2 PHYSICS: Electronics So what is a Capacitor? A Capacitor's Description: A capacitor consists of two or more plates of a conductive material separated by an insulating substance called a dielectric. A dielectric may be solid, gel, liquid, or gas. A capacitor's ability to store energy is measured in either microfarads (uF), nanofarads (nF), or picofarads (pF). Micro means one millionth, nano stands for one billionth, and pico for on trillionth (farads are also used, but in high voltage work they are impractically large units). Several factors affect capacitance. The formula for determining capacitance is: C = ε (A/d) Where C is the capacitance in picofarads, Permittivity (ε) is a measure of the ability of a material to be polarized by an electric field., A is the area of one conductive plate in square inches, d is the separation between adjacent plates in inches. As you may know, different insulators have different dielectric constants.

4. Capacitor construction Two metal plates Separated by insulating material ‘Sandwich’ construction Capacitance set by...

5. Defining capacitance ‘Good’ capacitors store a lot of charge… …when only a small voltage is applied Capacitance is charge stored per volt Capacitance is measured in farads F –Big unit so nF, mF and  F are used

6. A2 PHYSICS: Electronics Defining capacitance 1 farad is a very large unit. It is much more common to use the following: μF = 10 -6 F nF = 10 -9 F pF = 10 -12 F Q: A capacitor of capacitance 250 μF is connected to a battery of emf 6.0 V. Calculate: a) the charge on one plate of the capacitor Q = CV = 6 x 250 x 10 -6 = 1.5 x 10 -3 C

7. A2 PHYSICS: Electronics Parallel Combination The p.d. across each capacitor is the same. Q T = Q 1 + Q 2 Apply Q = CV to each capacitor to find C T. Q T = C 1 V + C 2 V Q T = V (C 1 + C 2 ) Q T / V = C 1 + C 2 C T = C 1 + C 2

8. A2 PHYSICS: Electronics Series Combination V T = V 1 + V 2 The charge, Q, on each capacitor is the same. Apply Q = CV to each capacitor. V T = Q/C 1 + Q/C 2 V T / Q = 1/C 1 + 1/C 2 1/C T = 1/C 1 + 1/C 2

9. A2 PHYSICS: Electronics Some Uses of Capacitors Defibrillators –When cardiac fibrillation occurs, the heart produces a rapid, irregular pattern of beats –A fast discharge of electrical energy through the heart can return the organ to its normal beat pattern In general, capacitors act as energy reservoirs that can be slowly charged and then discharged quickly to provide large amounts of energy in a short pulse