JEE Main20199 Jan 2019Morning ShiftPhysicsElectrostaticsActual

For a uniformly charged ring of radius R , the electric field on its axis has the largest magnitude at a distance h from its centre. Then value of h is:

Options

AR 2
BR 5
CR 2
DR

Correct answer

A. R 2

Step-by-step solution

Electric field at a distance h from centre on axis E = 1 4 π ε 0 Q h R 2 + h 2 3 2 To get maximum E , d E d h = 0 0 = 1 4 π ε 0 Q R 2 + h 2 3 2 - Q h 3 2 R 2 + h 2 1 2 2 h R 2 + h 2 3 ⇒ h = ± R 2

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