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Question: Answered & Verified by Expert
A uniformly charged thin spherical shell of radius R carries a uniform surface charge density of σ per unit area. It is made of two hemispherical shells, held together by pressing them with force F (see figure). F is proportional to


PhysicsElectrostaticsNEET
Options:
  • A 1ε0σ2 R2
  • B 1ε0σ2 R 
  • C 1ε0 σ2R
  • D 1ε0 σ2R2
Solution:
1846 Upvotes Verified Answer
The correct answer is: 1ε0σ2 R2
Electrical force per unit area

=12ε0E2

=12ε0σε02=σ22ε0

Projected area =πR2

∴ Net electrical force

=σ22ε0πR2

In equilibrium, this force should be equal to the applied force.

   F=πσ2R22ε0

Or Fσ2R2ε0

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