Current in the circuit

1. Jan 31, 2014

1/2"

1. The problem statement, all variables and given/known data
In the given circuit find the current i1,i2,i3.
(Image of the circuit is attached)

2. Relevant equations
current=(emf)/total resistance

3. The attempt at a solution
The original question actually asks me to find the currents using Kirchoff's laws .Since I feel this method to be a little tedious I tried to do it another way.
But the problem is the answers are not coming correct this way ,(which is as follows )

First since the two cells are connected opposite to each other i have assumed the resultant emf of the 21V to be 4V and I have neglected the other 17V cell.
then considering 2Ω and 5Ω resistances to be parallel to each other their resultant comes to be
(10/7)Ω .And this one being in series with 3Ω, The final resistance of the circuit comes out to be
(31/7)Ω.
Accordingly current should be i1=28/31 A
I am going seriously wrong somewhere:grumpy: , but can't figure out where. .

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Last edited: Jan 31, 2014
2. Jan 31, 2014

Tanya Sharma

What you have presumed would have been correct if the two batteries would have been in series .Do you think the batteries are in series ?

Please be careful ,there is a middle branch between the two batteries.The current flowing through them will not be the same .

Wrong .

Wrong .

3. Feb 2, 2014

Redbelly98

Staff Emeritus
You'll need to use Kirchhoff's rules here, tedious as they are.

As Tanya Sharma said, since the two batteries are not actually in series, you can't simply subtract their voltages.