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Two point charges -4 c and 4 c , constituting an electric dipole, are placed at (-9,0,0) cm and (9,0,0) cm in a uniform electric field of strength 10^4 NC ⁻¹ . The work done on the dipole in rotating it from the equilibrium through 180^ is :

Options

  1. A18.4 mJ
  2. B14.4 mJ
  3. C12.4 mJ
  4. D16.4 mJ

Correct answer

B. 14.4 mJ

Step-by-step solution

aligned & U =- PE & w _ ext = U = U _ f - U _ i =- PE 180^ + PE 0^ & w _ ext =2 PE & =2 (4 10⁻⁶ )(18) 10^4 & =144 10⁻² & =14.4 ~mJ aligned

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