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JEE Main 2020 (5 Sep, Shift 2) · Electric Field & Field Lines

Electric Field & Field Lines question from JEE Main 2020 (5 Sep, Shift 2)

Q36JEE Main 2020 · 5 SEP · SHIFT 2Medium

Electric Field & Field Lines

Ten charges are placed on the circumference of a circle of radius R with constant angular separation between successive charges. Alternate charges 1, 3, 5, 7, 9 have charge (+q) each, while 2, 4, 6, 8, 10 have charge (–q) each. The potential V and the electric field E at the centre of the circle are respectively.

(Take V = 0 at infinity)

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Answer: (a)

$V = \sum \dfrac{kq_i}{R} = \dfrac{k}{R}(5q - 5q) = 0$
The five $+q$ charges sit at the corners of a regular pentagon, so their fields at the centre cancel; the same holds for the five $-q$ charges.
So $E = 0$ .
So the answer is (a) $V = 0$ ; $E = 0$ .

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