Question

In the given circuit, assuming point A to be at zero potential, use Kirchhoff’s rules to determine the potential at point B.

Answer 1

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.