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Moving Charges And Magnetism

Question
CBSEENPH12037638

A charge 2Q is spread uniformly over an insulated ring of radius R/2. What is the magnetic moment of the ring if it is rotated with an angular velocity ω with respect to normal axis?

Solution
Given,
Radius of an insulated ring = R/2
Charge= 2Q
Angular 
velocity with which the ring is rotated with respect to normal axis = ω 

Now,

Charge on the element of length dl of the ring is
               dq = λ. dl 

           dq = 2Q2πR/2dl              = 2QπRdl 

Current due to circular motion of this charge is 

       dI = dq×v = 2QπRdl ×ω2π    ω = 2πv 

Magnetic moment due to current dl 

          dM = dI × π(R/2)2        = 2Qπrdl × ω2π×π(R/2)2  

            M = QωR4πdI     = QωR4π.2πR    = 12QωR2.