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JEE Main 2021 (26 Feb, Shift 1) · Electric Field & Field Lines

Electric Field & Field Lines question from JEE Main 2021 (26 Feb, Shift 1)

Q34JEE Main 2021 · 26 FEB · SHIFT 1Medium

Electric Field & Field Lines

Find the electric field at point P (as shown in figure) on the perpendicular bisector of a uniformly charged thin wire of length L carrying a charge Q. The distance of the point P from the centre of the wire is a = 32L\frac{\sqrt{3}}{2}L.

Figure

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Answer: (c)

  1. On the perpendicular bisector of a rod: E=kQaa2+L2/4E = \dfrac{kQ}{a\sqrt{a^2 + L^2/4}}.
  2. With a=32La = \dfrac{\sqrt3}{2}L: a2+L24=L2a^2 + \dfrac{L^2}{4} = L^2, so E=kQ(3L/2)LE = \dfrac{kQ}{(\sqrt3 L/2)L}.
  3. E=2Q4πε03L2=Q23πε0L2E = \dfrac{2Q}{4\pi\varepsilon_0\sqrt3 L^2} = \dfrac{Q}{2\sqrt3\pi\varepsilon_0 L^2}
  4. So the answer is (c).
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