IIT JEE , AIEEE Forum - Physics , Electricity - calculate equivalent capacitance...n plz explain it full....rates assured !!

netkid07

calculate equivalent capacitance for the arrangement given in the figure.....plz explain it fully....

netkid07

does that star delta conversion work for capacitors ??..howw ??

varun.tinkle

SUPPOSE A CHARGE

Q 1 ENTERS THE 5 CAPACITOR

AND Q 2 ENTERS THE 15 CAP

AND THE CURRENT Q1-Q3 ENTERS THE 25 CAPAC

THEN A CURRENT I3 ENTERS THE 10

AND A CURRENT Q1-Q3+Q1 ENTERS THE 20 CAPA

SUPPOSE A BATTERY IS CONNECTED ACROSS THE TERMINALS

THE POTENTIAL DIFFERENCE AT THE 5 CAP AND AT THE 15 IS V-V1

AND THAT AT THE 15 IS V-V2

AND BETWEEN THE 10 IS V1-0

AND BETWEEN THE 20 IS V2-0

APPLYING KIRCHOFFS LAW

POTENTIAL DIFFERENCE ACROSS A CLOSED LOOP IS 0

U CAN ALSO USE THIS METHOD\

THAT THE POTENTIAL DIFFERENCE BETWEEN THE 5 CAP AND 10 CAP = THE POTENTIAL DIFFERENCE BETWEEN THE 15 AND 20 CAP

THE EQUIV CAP CAN BE GIVEN FROM THIS EQUATION

C=Q/V

WHERE Q=Q1 +Q2

SOLVE IT AND FIND THE ANSWER

varun.tinkle

SUPPOSE A BATTERY IS CONNECTED ACROSS THE TERMINALS

SUPPOSE A CHARGE

Q 1 ENTERS THE 5 CAPACITOR

AND Q 2 ENTERS THE 15 CAP

AND THE CHARGE Q1-Q3 ENTERS THE 25 CAPAC

THEN A CHARGE Q3 ENTERS THE 10

AND A CHARGE Q1-Q3+Q1 ENTERS THE 20 CAPA

SUPPOSE A BATTERY IS CONNECTED ACROSS THE TERMINALS

THE POTENTIAL DIFFERENCE AT THE 5 CAP AND AT THE 15 IS V-V1

AND THAT AT THE 15 IS V-V2

AND BETWEEN THE 10 IS V1-0

AND BETWEEN THE 20 IS V2-0

APPLYING KIRCHOFFS LAW

POTENTIAL DIFFERENCE ACROSS A CLOSED LOOP IS 0

U CAN ALSO USE THIS METHOD\

THAT THE POTENTIAL DIFFERENCE BETWEEN THE 5 CAP AND 10 CAP = THE POTENTIAL DIFFERENCE BETWEEN THE 15 AND 20 CAP

THE EQUIV CAP CAN BE GIVEN FROM THIS EQUATION

C=Q/V

WHERE Q=Q1 +Q2

SOLVE IT AND FIND THE ANSWER

PLZ RATE ME IF U FIND ME USEFUL

!!!!!!!!!CHEERS!!!!!!!!!!!!

netkid07

could'nt understand a word.....plz solve it fully n gimme the answer....m getting 12.5 uf as the answer....

varun.tinkle

WHAT U DIDNT UNDERSTAND

netkid07

why r u goin wid these tedious n time consuming calculations.......just temme how to apply delta star conversion for capaciters.....n if possible....plz...gimme the answer....

varun.tinkle

U SEE MY METHOD IS ALL WRONG
U CAN USE THE CAPCITORS AS RESISTORS AND SOVE THE PROBLEM
USING KIRCOFFS LAW
THIS WOULD BE MUCH EASIER

netkid07

considering capaciters as resistors won't work coz resistance is'nt directly proportional to capacitance........

varun.tinkle

WIL SOLVE IT LATER

shikhar.jain50

the answer is 20/3 $\mu$ f .

v.sabarish

I can't give you the answer, but I can tell you what to do... I don't exactly know those star deltas or whatever........ Just one method would help you solve any problem..... I use just this one....
assume a charge Q1 on one of the left most plates....say on 5uF capacitor..... and charge on 15uF capacitor , on the left plate, is Q2
charges on the right plates of the 5 uF , 15 uF are then -Q1, -Q2

The positive charge, negative charge supplied by the batteries is the same in magnitude, so the net charge on the right plates of 10uF, 20uF must be equal to -(Q1+Q2)
assume some charges on them.....
now, the charge on top plate of 25uF is -(charge on right plate of 5uF+ charge on left plate of 10uF) and similarly charge on the bottom plate.....
you are left with 4 variables... charges on four outer capacitors.... one equation is obtd from the fact that charge supplied by positive terminal of batt= that by negative terminal in magnitude......
You get 3 more equations from the 3 loops in the connections, you solve them to get the answer

varun.tinkle

SEE DELTA STAR CONVERSION IS ONLY VALID FOR RESISTORS
WAIT FOR A FEW DAYS I AM TRYING TO CONVERT THE EQUATIONS FOR CAPACITORS
IT WILL TAKE SOME TIME COZ I AM CONVERTING ALL THE TRICKS FOR RESISTORS INTO CAPACITORS
I WILL POST MY RESULT IN THE COMMUNITY SHELF
TILL THEN
!!!!!!!!CHEERS!!!!!!!!!!!!!!!

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