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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:

1. R√(2)
2. R
3. R/√(5)
4. R/√(2)

Correct answer: R/√(2)

Solution

On the axis E ∝ x/(x^2 + R^2)^(3/2). Setting dE/dx = 0 gives x^2 = R^2/2, so the field is maximum at h = R/sqrt(2).

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