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Question: Answered & Verified by Expert
A little charged bead is inside the hollow frictionless sphere manufactured from the insulating material. Sphere has a diameter of 50 cm. The mass of the bead is 90 mg, its charge is 0.5  μC. What minimum charge must carry an object at the bottom of the sphere to keep hold the charged bead at the vertex of the sphere in stable equilibrium?
PhysicsElectrostaticsJEE Main
Options:
  • A 4.9×10-8  C
  • B 9.8×10-8  C
  • C 19.6×10-8  C
  • D 30.2×10-8  C
Solution:
2134 Upvotes Verified Answer
The correct answer is: 9.8×10-8  C





Let give small displacement to q . The equilibrium will be stable if net force after giving displacement will be in direction of position of equilibrium








Fesinαmgsin2α

then net force will be directed towards vertex i.e. initial equilibrium position

kqQd2  sinαmg sin2α

d=diameter  of sphere and  α  is very small

kqQd2×α mg×2α

Q2mgd2Kq=9.8×10-8C

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