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A charge Q is placed at the centre of a circle of radius 10 cm. Find the work done in moving a charge q between any two points lying on the arc of this circle.

Asked in GUJCET 2023 · Equipotential surfaces and V-r graphs

• (1) KQq J
• (2) 0.1 KQq J
• (3) 0.5 KQq J
• (4) 0 J

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives KQq; the radius has simply been dropped. In any case the work depends on the difference in potential between the two points, and every point on the circle is at the same (KQ)/r.
• (2) This multiplies by the radius, KQq×0.1, instead of dividing by it. And even (KQq)/r would be the potential energy at one point, not the work between two points at the same potential.
• (3) No single slip gives 0.5 KQq. Every point on the circle is at the same potential (KQ)/r, so the work between any two of them is zero.

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