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JEE Main 2019 (10 Jan, Shift 2) · Electrostatic Potential Energy

Electrostatic Potential Energy question from JEE Main 2019 (10 Jan, Shift 2)

Q53JEE Main 2019 · 10 JAN · SHIFT 2Medium

Electrostatic Potential Energy

Four equal point charges Q each are placed in the xy plane at (0, 2), (4, 2), (4, –2) and (0, –2). The work required to put a fifth charge Q at the origin of the coordinate system will be -

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Answer: (d)

  1. W=Q VoriginW = Q\,V_{origin}.
  2. Distances from origin: (0,±2)(0,\pm2) are 22; (4,±2)(4,\pm2) are 20=25\sqrt{20} = 2\sqrt{5}.
  3. V=Q4πε0(22+225)=Q4πε0(1+15)V = \frac{Q}{4\pi\varepsilon_0}\left(\frac{2}{2} + \frac{2}{2\sqrt{5}}\right) = \frac{Q}{4\pi\varepsilon_0}\left(1 + \frac{1}{\sqrt{5}}\right)
  4. W=Q24πε0(1+15)W = \frac{Q^2}{4\pi\varepsilon_0}\left(1 + \frac{1}{\sqrt{5}}\right), answer (d).
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