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JEE Main 2019 (10 Jan, Shift 1) · Electric Potential & Equipotentials

Electric Potential & Equipotentials question from JEE Main 2019 (10 Jan, Shift 1)

Q96JEE Main 2019 · 10 JAN · SHIFT 1Medium

Electric Potential & Equipotentials

A charge Q is distributed over three concentric spherical shells of radii a, b, c (a < b < c) such that their surface charge densities are equal to one another. The total potential at a point at distance r from their common centre, where r < a, would be -

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Answer: (d)

  1. Equal σ\sigma: q∝q \propto radius2^2, so qa=Qa2a2+b2+c2q_a = \frac{Qa^2}{a^2 + b^2 + c^2}, etc.
  2. For r<ar < a the potential is the sum of the shell surface potentials: V=k(qaa+qbb+qcc)V = k\left(\frac{q_a}{a} + \frac{q_b}{b} + \frac{q_c}{c}\right).
  3. V=Q(a+b+c)4πε0(a2+b2+c2)V = \frac{Q(a + b + c)}{4\pi\varepsilon_0(a^2 + b^2 + c^2)}
  4. So the answer is (d).
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