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Old Jun 19th 2009, 12:08 PM   #1
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question based on Kirchoff's laws

A cell supplies a current i1 through a coil of resistance R1,a current i2 through a coil of resistance R2.What is the e.m.f. and the resistance of the cell in terms of i1,i2,R1 and R2 ?


I guess this means the resistors are in parallel.So using ,Kirchoff's(hope I spelt it right) 2nd law,

E = (i1+i2)r + i1*R1
E = (i1+i2)r + i2*R2

(r is the internal resistance. E is the emf of the cell)

After equating the 2 equations,I get i1= (i2*R2)/R1
but I can't seem to get an expression for the emf without including 'r' in it.And when I tried to get an expression for r ,I end up including E in it.

Looking for some help here,
Thank you
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Old Jun 20th 2009, 03:57 AM   #2
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Well the question never mentions that the coils are in the same circuit or whether they are in series or parallel

If they are connected separately,
then
E=i1r+i1R1
E=i2r+i2R2
solve for E and r now

If they are in parallel, then

i1R1=i2R2
from the above equations,
i1=i2 n R1=R2
so u have only equation and 2 unknowns, so it is impossible to obtain unique values of E and r
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