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LAB 5Capacitors

OBJECTIVES1. Predict and measure the equivalent capacitance of capacitors connected in series

and parallel.

2. Predict and measure the voltages across capacitors in series and parallel.3. Investigate the capacitance of the electrometer.

EQUIPMENT

Capacitors (two each 0.0! F" 0.10 F# one 0.22 F and one 120 pF$" electrometer" %C

power suppl&" %''" readoard.

THEORY)n& arrangement that stores charge can properl& e called a capacitor. *he capacitance of

a capacitor is a measure of how much charge can e stored on the capacitor for agiven potential difference (voltage$. *he relation etween charge q" voltage +" andcapacitance C is given &

q C+.=

,hen two or more capacitors are connected together" the& ma& e replaced & a singlecapacitor that has the same capacitance (Ceq$ as the comination of capacitors. For twocapacitors connected in parallel" the equivalent capacitance is given &

eq 1 2C C C= + .

For two capacitors connected in series" the equivalent capacitance is given &

eq 1 21- C 1- C 1- C= + .

If a capacitor C1is connected to a power suppl& with voltage + 0" it will acquire a charge qgiven & q C1+0. If that capacitor is then disconnected from the power suppl& andconnected in parallel to an initiall& uncharged capacitor C2" the original charge q oncapacitor 1 is split etween the two capacitors. ,e therefore end up with the relation q q1/ q2" where q1and q2are the final charges on capacitors 1 and 2. ince capacitors 1 and 2

are in parallel" the& must have the same voltage +. *he relationship q q1/ q2thereforeecomes C1+0 C1+ / C2+.

PROCEDUREPart 1 E!"i#a$%&t Capacita&c%a. 'easure the individual capacitance values (using a %''$ of the following five

capacitors 0.0! F (two of them$" 0.01 F (two of them$ and 0.22 F.. sing the measured capacitance values" predict the equivalent capacitance (Ceq$th&of

Capacitors 0.01 F and 0.01 F in series

Capacitors 0.01 F and 0.01 F in parallel

) comination of two 0.10 F capacitors in series and parallel with a third 0.22 F

) comination of two 0.10 F capacitors in parallel in series with a third 0.22 F

capacitorc. 'easure the equivalent capacitance (Ceq$eptusing a %''. Compare (Ceq$th&and

(Ceq$eptusing a percent difference. ow dothe& compare4

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Part ' T(% Vo$ta)% across Capacitors*o measure the voltage across an initiall& uncharged capacitor" use the following procedure Connect a 0.0! F capacitor to a 10+ power suppl& and charge it up (one or two

seconds$. %isconnect the power suppl& from the capacitor and *% car%+"$ &ot to to"c(%it(%r si,% o+ t(% capacitor or -o" .i$$ ,isc(ar)% it/ Chec5 the voltage of thecapacitor and power suppl& using a electrometer.

,ith the charged 0.0! F capacitor" connect a second initiall& uncharged capacitor inparallel and charge it up.

se the electrometer to measure the voltage across the initiall& uncharged capacitorafter the two capacitors are connected in parallel/ Ma0% s"r% t(at -o" co&&%ct t(% t%r2i&a$ o+ t(% %$%ctro2%t%r to t(% p$at% o+ t(% 3/35 4capacitor ot(%r.is% -o".i$$ ,isc(ar)% t(% capacitor/ %ischarge all capacitors & touching oth plates of eachcapacitor at the same time with &our fingers.

For each of the capacitor configurations listed elow" predict (+th&$ and measure (+ept$ thevoltage across the initiall& uncharged capacitor will read after the two capacitors areconnected in parallel. Compare +th&and +eptusing a percent difference.

a. *he initiall& uncharged capacitor is a single 0.0! F capacitor.

. *he initiall& uncharged capacitor is a single 0.10 F capacitor.

c. *he initiall& uncharged capacitor is two 0.10 F capacitors in parallel.

d. *he initiall& uncharged capacitor is two 0.10 F capacitors in series.

Part 6 Pr%,icti&) a&, M%as"ri&) t(% E!"i#a$%&t Capacita&c%sing the procedure of Part 2" predict the equivalent capacitance (Ceq$th&& measuring thevoltage across the initiall& uncharged capacitor after the two capacitors are connected inparallel. Compare (Ceq$th&and (Ceq$ept(from Part 1$ using a percent difference.a. *he initiall& uncharged capacitor is a comination of two 0.10 F capacitors in series

and parallel with a third 0.22 F capacitor.

. *he initiall& uncharged capacitor is a comination of two 0.10 F capacitors in parallel inseries with a third 0.22 F capacitor.

Part 7 Capacita&c% o+ t(% E$%ctro2%t%r

a. old a 1'3 p4capacitor as shown & the instructor and then connect the capacitor tothe power suppl&. )fter the capacitor is full& charged (one or two seconds$" disconnectthe power suppl&.

. Predict what the voltage across the 120 pF capacitor will e when &ou read the voltageusing the electrometer.

c. se the electrometer to measure the voltage across the 120 pF capacitor. ,as &ourprediction correct4 6eport on &our results and an& possile reasons for thediscrepanc&.

d. se &our results from part (c$ to calculate the capacitance of the electrometer.

e. ,h& didn7t the capacitance of the electrometer have a noticeale effect on the resultsfrom Parts 2 8 34

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Predict and measure the voltage across the initiall& uncharged 0.10 F capacitor will readafter the two capacitors are connected in parallel. Compare + th&and +eptusing a percentdifference.

c. Predict (+th&$ and measure (+ept$ the voltage across the two initiall& uncharged 0.10 Fcapacitor will read after the two capacitors are connected in parallel. Compare + th&and+eptusing a percent difference.

d. Predict (+th&$ and measure (+ept$ the voltage across the two initiall& uncharged 0.10 Fcapacitor in parallel will read after the two capacitors are connected in parallel.Compare +th&and +eptusing a percent difference.

e. Predict (+th&$ and measure (+ept$ the voltage across the two initiall& uncharged 0.10 Fcapacitor in series will read after the two capacitors are connected in parallel. Compare+th&and +eptusing a percent difference.