Exp 5

Electric lab

:Objective . determine and measurre RC time constant _1 familiarization with the structure of the _2 . capacitor and properties .familiarization with time constant concept _3 familiarization with the behavior of the capacitor _4 during the processes of charging and .discharging familiaraization with parallel and series networks_5 . of capacitor familiraization with methods of measurement in_6 .resistor-capacitor (RC)networks to learn calculate the effective value of the -7 .capacitor in series and parallel : Theory V=Q /C : Charging capacitor /

V(t)=Vs(1-e-t

/

I=Imax e-t

, Imax =Vs/R At Vc=0.63Vs , I=0.37Imax : Discharging capacitor

Electric lab /

Vc(t)=Vs e-t

/

I(t)=Imax e-t

The effective value of the capacitors in the :series Ceq=(c1*c2)/(c1+c2 )…..series Ceq=c1+c2 ……………..parallel

:(result and digrams(data of table :table 1 Number of time constant

Measured quantity Charging (time (sec

Measured (voltage (V

Calculated (voltage (v

Calculated (current (µA

0.5

5.875

12.6

13.77032635 40.12

1

11.75

18.3

22.12288447 27.37

1.5

17.625

25.2

27.18922971 16.6

2

23.5

28

2.5

29.375

30.6

3

35.25

31.4

33.2569105 3.7

3.5

41.125

31.6

33.94270796 2.24

4

47

32.5

34.35868672 1.36

4.5

52.875

32.6

34.61100367 0.826

5

58.75

32.8

34.76404956

30.26228274 10 32.12628025 6.108

0.501

Electric lab

: Question From the value recorded in table ,draw the capacitor charging curve (voltage and ?(current

Electric lab

:Table 2 Number of time constant

Measured quantity discharging (time (sec

Measured (voltage (V

Calculated (voltage (v

Calculated (current (µA

0.5

5.875

16.4

21.22967365 40.12

1

11.75

8.5

12.87711553 27.37

1.5

17.625

5.7

7.810770292 16.6

2

23.5

3.4

4.737717265 10

2.5

29.375

2.1

2.873719754 6.108

3

35.25

1.2

1.743089501 3.7

3.5

41.125

0.8

1.057292036 2.24

4

47

0.5

0.641313282 1.36

4.5

52.875

0.3

0.388996334 0.826

5

58.75

0.2

0.235950435

:Table 3

0.501

Electric lab

(C2(µF

(C3 (µF

Calculated effective capacitance ((µF

Time constant ((sec

Weasured effective capacitance ((µF

25

25

12.5

6.73

14.25

(C2(µF

(C3 (µF

Calculated effective capacitance ((µF

Time constant ((sec

Weasured effective capacitance ((µF

25

25

50

25.4

54.04

:Table 4

: Question describe the process of charging and discharging a-1 ? capacitor Whine the charging the capacitor start the current the maximum but the voltage start the minimum , equal zero Whine the discharging the capacitor start the current . the maximum and the voltage it is maximum ?..………… what is the time constant ?is there -2 The time constant is the product of the resistor in the circuit and the capacitor ,not there difference between the charging time constant and the discharging time constant because value the .capacitor and the resistor constant …… what is an electrolytic capacitor ? why must -3 ?.…

Electric lab

compare the equation for the effective value of-4 ?.…… capacitor . Not equal the common to them it is capacitor

: Calculation Vs=35*(1-e-5.875/11.75)) =13.77v ………………… charging Imax=35/470k =0.0744mA I=0.0744*10-3(e-5.875/11.75)=40.12 µA…charging .and discharging Vs=35*(e-5.875/11.75))=21.22v ………………. discharging 470k*25 µf =11.75 s =

Ceq=(25*25)/25+25=12.5µf R*C=6.73=470k*Ceq= Ceq=6.73/470k =14.3µf

Ceq=25+25=50µf 470k*Ceq=25.4

Electric lab

Ceq=54.04µf 35v=22v*0.63

: Conclusions the time constant is constant charging and-1 . discharging the effective in the capacitor contrary to the-2 .resistor