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JA-622 Lesson 3: Capacitors

JA-622 Lesson 3: Capacitors. What are capacitors? How are they used? How are they made? What are their sizes? What is an RC time constant?. (1663) Guericke invents friction based spark generating machine. http://en.wikipedia.org/wiki/Otto_von_Guericke.

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JA-622 Lesson 3: Capacitors

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  1. JA-622 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 http://en.wikipedia.org/wiki/Otto_von_Guericke

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

  4. Let’s make a capacitor http://sci-toys.com/scitoys/scitoys/radio/homemade_radio.html

  5. Rolling our capacitor http://sci-toys.com/scitoys/scitoys/radio/homemade_radio.html

  6. The finished capacitor http://sci-toys.com/scitoys/scitoys/radio/homemade_radio.html

  7. How capacitors work? Ic = 0 Ic +Q = 0 +Q +Q ++++++ ++++++ Vs Vs Vs Electric Field Electric Field Vc = 0 Vs or Vc - - - - - - - - - - - - - - -Q = 0 -Q -Q electrons C = capacitance (farads) Q = electron or ion charge on metal plates (coulombs) Ic = current (amps) Vs = DC voltage source (battery voltage)

  8. What are capacitors?

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

  10. + + Let’s experiment with a capacitor (ckt 3-1) 1K W 9 volts 4700 uf LED Adapted from Discover Electronics: Mr Circuit One, Electronic Kourseware Interactive, 2002 (www.EKII.com)

  11. Hook up diagram for ckt 3-1 push button switch 1K + + 9.0 volts Long lead of LED (+) goes up. LED 4700 uf

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

  13. + + Capacitor discharge after one time constant (ckt 3-2) 4700 uf VOM 9 volts

  14. Hook up diagram for ckt 3-2 push button switch Volt Meter :10 vdc R + + 9.0 volts 4700 uf

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

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