Physics Help Forum question based on Kirchoff's laws

 Electricity and Magnetism Electricity and Magnetism Physics Help Forum

 Jun 19th 2009, 12:08 PM #1 Member   Join Date: Jun 2009 Posts: 79 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
 Jun 20th 2009, 03:57 AM #2 Senior Member   Join Date: May 2009 Location: Mumbai,India Posts: 102 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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### a cell supplies the current I1 through a resistance R1 and a guy current I2 through a resistance are to the internal resistance is

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