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Question
In the given circuit, assuming point A to be at zero potential, use Kirchhoff’s rules to determine the potential at point B.
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Solution
According to Kirchhoff’s Junction Law, when applied at junction D:
Incoming current = outgoing current
So, 3A = 1A + current through 2Ω.
Hence, current through 2Ω is 2A from D to C. Applying Kirchhoff’s law to the loop containing R1, 2Ω and 4V.
3A is the current through R1 as the current coming out from the 4V battery is 3A.
4 = 3 × R1 + 2 × 2
⇒ R1 = 0 Ω
So, no potential drop between B and C.
Now lets analyse the bigger loop containing 4V, R and 2V (R1 can be omitted now); here the 4V and 2V are connected in series with B as a point between the two batteries. So we finally have the potential at B to be 2V.
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