7/24/2019 phy. lab 5

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Objective

Familiarization with charging and discharging process, time constant

concept and series-parallel connection.

Theory

A capacitor(originally known as a condenser) is a passive two-terminal electrical

component used to store electrical energy temporarily in an electric field. The forms

of practical capacitors vary widely, but all contain at least two electrical conductors

(plates) separated by a dielectric (i.e. an insulator that can store energy by becoming

polarized). The conductors can be thin films, foils or sintered beads of metal or

conductive electrolyte, etc. The nonconducting dielectric acts to increase the

capacitors charge capacity. A dielectric can be glass, ceramic, plastic film, air,

vacuum, paper, mica, o!ide layer etc. "apacitors are widely used as parts of electrical

circuits in many common electrical devices. #nlike a resistor, an ideal capacitor does

not dissipate energy. $nstead, a capacitor stores energy in the form of an electrostatic

field between its plates.

%hen there is a potential difference across the conductors (e.g., when a capacitor is

attached across a battery), an electric field develops across the dielectric, causing

positive charge &Qto collect on one plate and negative charge 'Qto collect on the

other plate. $f a battery has been attached to a capacitor for a sufficient amount of

time, no current can flow through the capacitor. owever, if a time-varying voltage is

applied across the leads of the capacitor, a displacement current can flow.

Equipment

DC source, decade resistor box, two capacitor, stop watch and

multimeter.

Procedure

A. Charging Process

1 Connect the circuit as shown in figure(5.! with " # 1$%.& Close switch '1and measure the capacitor oltage eer) 1*

seconds.+ Calculate the capacitor oltage and current for the gien

periods of time. lot the capacitor charging cure (oltage and current!.

B. Discharging Process

1 Connect the circuit as shown in figure(5.! with " # 1$%.

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& /pen '&and close '1for two minutes. During this time, the

capacitor will be charged.+ /pen '1and close '&. $easure the oltage across the

capacitor eer) 1* seconds. Calculate the capacitor oltage and current for the gien

periods of time.5 lot the capacitor charging cure (oltage and current!.

C. Series Connection

1. Connect the circuit shown in 0gure (5.!&. Close '1and measure the time re2uired for the capacitors to

charge to a oltage e2uals +3 times the alue of the oltage

source.+. Calculate the e4ectie capacitance.

. sing the measured time constant, 0nd the e4ectiecapacitance where ! "Ce#.

D. Para$$e$ Connection

1. Connect the circuit as shown in 0gure (5.6!&. Close '1measure the time re2uired for the capacitors to

charge to a oltage e2uals +3 times the alue of the oltage

source.

+. Calculate the e4ectie capacitance.. sing the measured time constant, 0nd the e4ectie

capacitance where ! "Ce#.

"esu$t7able(5.1!8 Charging of Capacitor

Charging

time(sec.!

$easured

oltage(9!

Calculated

oltage(9!

Calculated

current(:;!1* 15. 15. 6.16&& 16.* &1.1 +.++* 16.* &+.5 1.&

* 16.&6 &.5 *.55* 16.&6 &.+ *.1* 16.&6 &.6+ *.** 16.+ &.6 *.*&&* 16. &.66 *.**6* 16. &.66 *.**+1** 16. &.66 *.**1

Consider t # 1*sec, < # &59, = # 1*sec.

Calculated oltage(9! # < ( 1-e-t>"C!

# &5 ( 1-e-1*>1*!

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# 15.9

* &* * * * 1** 1&*

*

5

1*

15

&*

&5

Figure 1 8 Charging of Capacitor (oltage-time relationship!

* &* * * * 1** 1&*

*

&

1*

Figure & 8 Charging of Capacitor (current-time relationship!

7able(5.&!8 Discharging of CapacitorCharging

time(sec.!

$easured

oltage(9!

Calculated

oltage(9!

Calculated

current(:;!

1* .+ 6.16 6.16&* +.* +.+ +.++* 1. 1.& 1.&* *. *.5 *.55* *.+ *.1 *.1* *.1 *.* *.** *.* *.*&& *.*&&* *.*6 *.** *.**6* *.*+ *.**+ *.**+1** *.*& *.**1 *.**1

Consider t # 1*sec, < # &59, = # 1*sec.

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Calculated oltage(9! # < e-t>"C

# &5 e-1*>1*

# 6.169

* &* * * * 1** 1&*

*

1

&

+

5

Figure + 8 Discharging of Capacitor (oltage-time relationship!

* &* * * * 1** 1&*

*

1

&

+

5

6

1*

Figure 8 Discharging of Capacitor (current-time relationship!

7able (5.+! 8 'eries Connection

C1(:F! C&(:F!

Calculated

e4ectie

capacitance(

:F!

7ime

constant(se

c.!

$easured

e4ectie

capacitance(

:F!1* 1* 5 .5 .

7able (5.! 8 arallel Connection

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C1(:F! C&(:F!

Calculated

e4ectie

capacitance(

:F!

7ime

constant(se

c.!

$easured

e4ectie

capacitance(

:F!

1* 1* &* &. &.