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capacitor

capacitor. They are important in both electric & electronic circuit. Have you seen any of them before ?. Where can we find the capacitors ?. We can find it in radio, TV sets , and computers .

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capacitor

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  1. capacitor

  2. They are important in both electric & electronic circuit • Have you seen any of them before ?

  3. Where can we find the capacitors ? We can find it in radio, TV sets , and computers .

  4. Although there are many different types of capacitors , but they all work in the same way , and that which make it easy to use .

  5. Function : • Capacitors can store and then release electrical energy . • The value of a capacitors is often measured in micro-farads . • The amount of energy stored by the capacitor depends on : How much charged is moved on to the plates . properties

  6. All the capacitor have two leads the leads connect to two plates ,the conducting plates are separated by an insulating material which called the dielectric

  7. The pates in capacitor need to have quite a large area • How is this achieved • By makes the insulator rolled up

  8. Capacitors • In its simplest form, a capacitor consists of two metal plates, separated from each other by an insulator (air, mica, paper etc.) • A charged capacitor is shown below. • The capacitor plates have an equal but opposite charge of magnitude Q. • The net charge on the two plates is zero. + Q +++++++ - Q -------

  9. Charging a capacitor :What happens when the switch closed ?

  10. Discharging capacitor :if the battery is removed , we can discharge the capacitor + _

  11. The charging & discharging processes happen very quickly .Can we show them down ?

  12. Chart Q Charging Q Discharging t t

  13. Why does the direction of charging current in the opposite way of current of the battery ?

  14. Q • Why current equal zero ? • Because p.d of battery =p.d of capacitor but in opposite direction

  15. The charging & discharging processes happen very quickly .Can we slow them down ? • (if we place a resistor in series with capacitor the capacitor charge and discharges more slowly • Also we put a variable resistor to keep the current in steady value

  16. Capacitance • The ability of a capacitor to store charge on its plates.

  17. The large the capacitance , the more charge the capacitor stores for each volt applied across its plates . In fact : • Capacitance = charge / voltage • C = Q / V • Solve example1 page 267

  18. How can we measured the charge on the capacitor plates ? i.t=q

  19. Measuring capacitance :

  20. Complete the table :

  21. A B

  22. Questions : • Q1:What happens to the capacitor when the switch in position A? • Q2:What happens if you move the switch to position B? • Q3:Where did this energy come from ?

  23. The energy of a charged capacitor • The p.d. across the capacitor and the size of its capacitance , both affect the energy stored . • Energy stored =0.5Xcapacitance X (voltage)2 W = 0.5 X C X V2 OR W = 0.5 X Q X V

  24. Q1 • A capacitor is charged using a current of 20µA from a 5volts supply .After 55s it is fully charged. • Calculate : • A. Q? • B. C? • C. W?

  25. Use these link to find more about our lessons • http://electronics.howstuffworks.com/solid-state-electronics-channel.htm http://us.c2w.com/quizzes/45045-capacitor-quiz

  26. Capacitor in parallel

  27. Here are 3 facts that you should know for capacitors in parallel • The p.d. across each capacitors is the same & equal to V . • The total Q is the sum Q = Q1+Q2 • The total C is the sum C = C1+C2 Q = C V

  28. Capacitor in series

  29. Here are 3 facts that you should know for • The Q. across each capacitors is the same & equal to Q . • The total V is the sum V= V1+V2 • The total C is the sum 1/C = 1/C1+ 1/C2

  30. Qs. • Q1: Calculate the charge on each capacitor in this diagram : • If : • V=5volt • C1=500 micro farad C2=300 micro farad

  31. Home Work : Pg. 273 , Q :1-3-4-5-6

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