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In the part of a circuit shown in the figure, the potential difference between the two points A and B is V_B - V_A = ____.

Asked in GSEB Board July 2022 · Kirchhoff's laws in networks

Figure: Kirchhoff's laws in networks
Answer: (2) IR - V

Step-by-step solution

Given (figure): starting from A there is a cell of emf V with its + plate toward A, then a resistor R, then B; the current I flows from B toward A.

Idea: walk from A to B adding up the potential changes.

Across the cell, from + to -: the potential falls by V.

Across the resistor, against the current: the potential rises by IR, because current flows from higher to lower potential.

V_A - V + IR = V_B, so V_B - V_A = IR - V.

So V_B - V_A = IR - V.

Why the other options are wrong

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