CBSE Class 12-science Answered

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A charged disc rotating at constnt angular velocity is equivalent to a steady current in circular wire. We need to calculate this current to find the magnetic field. Let us consider any one cross-section of the wire and all charges must pass through this crosssection in one time period of revolution.

Hence current is:

I = q/T = q (ω / 2π)

Magnetic field due to steady current in a circular wire is:

B = µ_oI / 2R

Substituting for current , we have,

B = µ_oqω / 4πR