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Electricity

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21 Mar 2008 05:12:21 IST

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plz help

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A capacitor of 4microfarad charged to 50v is connected to another capacitor of 2 micro charged to 100v.total energy of the combination is?
ans is 4/3*10^-2j

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Gaurav |spideyunlimited| Ragtah

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21 Mar 2008 05:46:01 IST

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First , always remember that if 2 capacitors are connected to each other (no cell present) then the 2 are considered to be in parallel.

Also E = Q^2 / 2C

Q1 = C1 V1 = 4 x 10^-6 * 50 = 2 x 10^-4 C

Q2 = C2 V2 = 2 x 10^-6 * 100 = 2 x 10^-4 C

Q = Q1 + Q2 = 4 x 10^-4 C

C = C1 + C2 = 6 x 10^-6 F

Now -
E = Q^2 / 2C = (4 x 10^-4) ^2 / 2 x ( 6 x 10^-6)
= (4/3) x 10^-2 Joules

suresan

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Joined: 10 Mar 2008

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21 Mar 2008 10:36:43 IST

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But there is one more option i think, since it is not well specified. The capcitors can also be connected anti-parallel. That is +ve plate of the first capacitor is connected to the -Ve plate of the second capacitor.

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