PRESENTATION ON CAPACITERS.

1. Saima AsgharRoll No.07-20Mudassir AbbasRoll No.07-34Aliya AshrafRoll No.07-19Shafaq MehmoodRoll No.07-02

2. PRESENTATION ONCAPACITERS. CONTENTS. 1.History 2.Theory of operation 3.Capacitance 4.Energy storage 5.Eletric circuits 6.Dc source 7.Ac source

3. HISTORY • In October 1745, Ewald Georg von Kleist of Pomerania in Germany invented the first recorded capacitor: a glass jar with water inside as one plate was held on the hand as the other plate. A wire in the mouth of the bottle received charge from an electric machine, and released it as a spark.

4. In the same year, Dutch physicist Pieter van Musschenbroek independently invented a very similar capacitor. It was named the Leyden jar, after the University of Leyden where van Musschenbroek worked. Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity.

5. Theory of operation. A capacitor consists of two conductive electrodes, or plates, separated by a dielectric, which prevents charge from moving directly between the plates. Charge may however move from one plate to the other through an external circuit, such as a battery connected between the terminals.

6. Dielectric Dielectric is placed between two conducting plates, each of area A and with a separation of d. . The simplest practical capacitor consists of two wide, flat, parallel plates separated by a thin dielectric layer.

7. Capacitance • A capacitor's ability to store charge is measured by its capacitance , the ratio of the amount of charge stored on each plate to the voltage: :

8. EQUATION • For an ideal parallel plate capacitor with a plate area and a plate separation :

9. Energy Storage When capacitor is uncharged,the potential diff. between plates is zero & finaly becomes V than Q charges is deposited on each plate thus the average potiential diff. is 0+V/2=1/2V

10. There for • P.E=Energy=1/2qV • Using the relation q=CV for capacitor we get • Energy=1/2CV2

11. Electric circuits • When a capacitor is connected to a current source, charge is transferred between its plates at a rate i(t) = dq(t) / dt. As the voltage between the plates is proportional to the charge, it follows that

12. Conversely, if a capacitor is connected to a voltage source, the resulting displacement current is given by

13. For example, if one were to connect a 1000 µF capacitor to a voltage source, then increase the sourced voltage at a rate of 2.5 Volts per second, the current flowing through the capacitor would be

14. DC sources A simple resistor-capacitor circuit demonstrates charging of a capacitor.

15. AC sources • When connected to an alternating current (AC) voltage source, the voltage across the capacitor varies sinusoidally as • v(t) = V0sin(ω0t + φ),

16. where ω0 = 2πf0 is the angular frequency of the source, V0 is the amplitude of the voltage and φ is the phase. The corresponding displacement current is therefore

17. MUDASSIR ABBASROLL NO. 07-34

18. Capacitors • Basic capacitor construction Dielectric material The dielectric material is an insulator therefore no current flows through the capacitor Plate 2 Plate 1

19. Capacitors Storing a charge between the plates • Electrons on the left plate are attracted toward the positive terminal of the voltage source • This leaves an excess of positively charged holes • The electrons are pushed toward the right plate • Excess electrons leave a negative charge _ + _ + - +

20. Effect of Area on Capacitance • Capacitance is directly proportional to the amount of charge. • A larger plate will be able to hold more charge. • Capacitance is directly proportional to the plate area. • If you double the plate area, you double the capacitance.

21. Effect of Spacing on Capacitance • As plates are moved closer together, the force of attraction between the opposite charges is greater. (Electrostatic field increases) • Capacitance is inversely proportional to the distance between the plates. • If we double the distance between the plates, the capacitance becomes one-half as much.

22. Effect of Dielectric on Capacitance • If a dielectric other than air is used between the plates, more charges can build up on the plates. • The factor by which the capacitance increases is called the dielectric constant or the relative permittivity. • Permittivity is the measure of how easy it is to establish or concentrate electric flux in a material. • Leakage current is the small amount of current that passes or flows through the dielectric without damaging the dielectric. • The type of dielectric used determines the permittivity and leakage current in a capacitor.

23. Common Dielectrics

24. Capacitors In Series When the capacitors are connected in series, the total capacitance is less than the smallest capacitance value bcoz the effective plate separation increases.

25. Continue…. • Series connected Capacitors always have the same Charge. They do not the same voltage unless the capacitors have the same Capacitance C. • The Charge on the equivalent capacitor Ce is the same as the charge on either capacitor. • The Voltage across the equivalent capacitor Ce is the sum of the voltage across both capacitors.

26. Continue….

27. Continue…. Consider a circuit having cap in series Qtot = Q1 = Q2 =Q3………. =Qn----( 1 Acc to Kirchhoff’s law Vt = V1+V2+V3+V4………….+Vn------(2 We know that V = Q / C Substituting the values…..

28. Continue.. Qt/Ct = Q1/C1+Q2/C2+Q3/C3+…..Qn/Cn Charge on all Cap are equal,so Q can B cancalled SO 1/Ct=1/C1+1/C2+1/C3+….1/Cn Taking the reciprocal Ct=1/1/C1+1/C2+1/C3+……1/Cn RESULT: Total series capacitance is always less than the smallest capacitance.

29. Continue.. When 2 capacitors R connected in series.. Then 1/Ct= 1/C1 + 1/C2 • C1+C2/C1C2 Taking Reciprocal Ct = C1C2/C1+C2

30. Capacitors In Parallel When cap R connected in ||,the total capacitance is the sum of the individual capacitance bcoz the effective plate area increase.

31. Continue..

32. Continue.. According 2 kirchhoff’s rule, Qt = Q1+Q2+Q3+…….Qn -------(1 We also know that Q = CV -------( 2 Then CtVt = C1V1+C2V2+C3V3+……..CnVn---( 3 Since V is same So it could B cancalled,

33. Continue… Then 3 becomes: Ct = C1+C2+C3+……………C RESULT: The total parallel capacitance is the sum of all the capacitors in parallel.

34. Capacitance of A ||Plate Capacitor. Consider a capacitor of 2 plates,each of area A, separated by a distance d,the dist is so small so the Electric Field E b/w the plates is uniform.Let the medium B air or vacuum. C = Q/V --------- ( 1 Q is charge V is Potential Diff..

35. Continue….. The Electric Intensity E is related with distance d, E = V/d ------------( 2 Surface Density of charge on the plates is σ = Q/εA -----------( 3 We know that electric Intensity b/w 2 opposite charged plates is E =σ /ε----------------( 4

36. Continue….. Substituting the Values… V/d = Q/A ε-----------------( 5 Gives… C = Q/V = A ε/d --------------------( 6

37. TYPES OF CAPACITORS

38. (a) Polyester capacitor, (b) Ceramic capacitor, (c) Electrolytic capacitor

39. VARIABLE CAPACITOR Variable capacitors

40. APPLICATIONS OF CAPACITORS

41. Temporary power source A capacitor provides “V” & “I” as long as its charge remains sufficuent.As current drawn by the circuit charge is removed from the capacitor & the voltage decreases. For this reason,the storage capacitor can B used as Temporary power source…

42. Computer Memories Dynamic memories in computers use very tiny capacitors as the basic storage element for binary info,1s & 0s. A charged capacitor can represent a stored 1, & discharged capacitor stored 0.

43. Signal Filter Capacitors are essential to the operation of a class of a circuit called FILTER.That are used for selecting one ac signal with a certain specified frequency from a wide range of signals. Common example is when U tune Ur radio or TV.

44. Variable Capacitors • Used to tune a radio. • Have a set of stationary plates and a set of movable plates which are ganged together and mounted on a shaft. • A trimmer or padder capacitor is used to make fine adjustments on a circuit.

45. ANY