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The figure shows the field lines of a positive and a negative charge respectively. Give the signs of the potential differences V_Q - V_P and V_B - V_A.

Asked in GSEB Board March 2023 · Relation between field and potential

Figure: Relation between field and potential
Answer: (1) negative, positive

Step-by-step solution

Idea: the potential of a point charge is V = 1/(4πε₀)q/r, and it always falls along the direction of the field lines.

Figure (a), charge +q: P is nearer the charge than Q, so V_P > V_Q (going from P to Q we move with the field).

Hence V_Q - V_P is negative.

Figure (b), charge -q: A is nearer the charge than B, so V_A is more negative than V_B (going from B to A we move with the field).

Hence V_B - V_A is positive.

So the signs are negative, positive.

Why the other options are wrong

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