Home Physics Electrostatics Potential & Capacitance Self Energy and Energy Density Two concentric spherical shells of radius R …
Physics Electrostatics Potential & Capacitance Self Energy and Energy Density Subjective Type
Published on: September 11, 2026

Two concentric spherical shells of radius R 1 and R 2 (R 2 > R 1 ) are having uniformly distributed charges Q 1 and Q 2 respectively. Find out total energy of the system.

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Verified by Experts
The correct answer is:
B
To find the total energy of the system of two concentric spherical shells with radii R1 and R2 and charges Q1 and Q2, we will consider the energy stored in the electric fields created by these charges.
  • Step 1: The potential due to a uniformly charged spherical shell at a point outside the shell (radius > R) is given by:
  • V = \frac{1}{4\pi\epsilon_0} \frac{Q}{r}

  • Step 2: For the inner shell with charge Q1 at radius R1, the potential at the radius R2 (where the outer shell is) is:
  • V_{1}(R_{2}) = \frac{1}{4\pi\epsilon_0} \frac{Q_{1}}{R_{2}}

  • Step 3: The energy U1 of the charge Q2 in the potential V1 is given by:
  • U_{1} = Q_{2} V_{1}(R_{2}) = Q_{2} \left( \frac{1}{4\pi\epsilon_0} \frac{Q_{1}}{R_{2}} \right)

  • Step 4: Now, we need to calculate the energy U2 of Q1 in the potential due to Q2 at radius R1:
  • V_{2}(R_{1}) = \frac{1}{4\pi\epsilon_0} \frac{Q_{2}}{R_{1}}

  • Step 5: The energy U2 is:
  • U_{2} = Q_{1} V_{2}(R_{1}) = Q_{1} \left( \frac{1}{4\pi\epsilon_0} \frac{Q_{2}}{R_{1}} \right)

  • Step 6: Adding these two energies gives the total energy of the system:
  • U_{total} = U_{1} + U_{2} = Q_{2} \left( \frac{1}{4\pi\epsilon_0} \frac{Q_{1}}{R_{2}} \right) + Q_{1} \left( \frac{1}{4\pi\epsilon_0} \frac{Q_{2}}{R_{1}} \right)

  • Final Answer: Thus, the total energy of the system is:
  • U_{total} = \frac{1}{4\pi\epsilon_0} \left( \frac{Q_{1}Q_{2}}{R_{2}} + \frac{Q_{2}Q_{1}}{R_{1}} \right)

Therefore, B is the correct answer.

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