A thin circular disk of radius R is uniformly charged with density σ 0 per unit area. The

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A thin circular disk of radius R is uniformly charged with density &#0963; > 0 per unit area. The disk rotates about its axis with a uniform angular speed &#969;. The magnetic field at centre of the disk is :-

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Let a ring of radius x and width dx.Assume charge on ring is dqArea of ring dA = 2&#960; x dx&#0963; = &#8658; dq = &#0963;2&#960; x dxCurrent due to this ring dI = dI = &#969; &#0963; x dxMagnetic field due to ring at centre dB = = &#956;0&#0963;&#969;dxMagnetic field due to disc at centreB =&#956;0&#0963;&#969; &#956;0 &#0963;&#969;R

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