1. BE Lesson 3: Capacitors What are capacitors? How are they used? How are they made? What are their sizes? What is an RC time constant?

2. (1663) Guericke invents friction based spark generating machine 

3. Peter van Musschenbroek’s “Leyden Jar” (an early version of a capacitor) Metal Ball

4. BE demo 3-1. James Wimshurst’s electrostatic generator (1883) with Peter van Musschenbroek’s Leyden Jar (1745) ES demo 2-6

5. What are capacitors?

6. How capacitors work? Vs V c = 0 +Q = 0 -Q = 0 I c = 0 C = capacitance (farads) Q = electron or ion charge on metal plates (coulombs) I c = current (amps) Vs = DC voltage source (battery voltage) Vs ++++++ - - - - - - - VcVc Electric Field +Q -Q electrons Vs ++++++ - - - - - - - V s or Electric Field +Q -Q IcIc

7. Capacitor come in a large range of sizes. 1 micro-Farad = 1  F = 10 ^-6 farad = (1/1,000,000) Farad 1 nano-Farad = 1 nF = 10 ^-9 farad = (1/1,000)  F 1 pico-Farad = 1 pF = 10 ^-12 farad = (1/1,000) nF

8. BE ckt 3-2. Observe how a capacitor operates + + 4700 uf  volts LED 220  Adapted from Discover Electronics: Mr Circuit One, Electronic Kourseware Interactive, 2002 (www.EKII.com)

9. BE ckt 3-2 hookup diagram Normally open (NO) push button switch + 4700 uf 220 LED + 9.0 volts Long lead of LED (+) goes up. + ES ckt 8-2

10. What is an RC time constant (  sec  ? After one time-constant (  ), the capacitor is ~ 63% discharged. After 5 time-constants (5  ), the capacitor is ~ 99% discharged. This chart will help us choose the size capacitors and resistors for later projects.

11. BE ckt 3-3. Time constants for two example resistors + + 4700 uf VOM 9 volts

12. BE ckt 3-3 hookup diagram push button switch + 4700 uf R + 9.0 volts :20 vdc Volt Meter ES ckt 8-4

13. What if we need a special size capacitor? How to calculate size if in series or parallel.