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Moving Charges And Magnetism

Question
CBSEENPH12037661

Obtain an expression for the magnetic moment associated with the orbital motion of an electron.

Solution

Consider, a stationary heavy nucleus around which an electron is performing a uniform circular motion. 
Charge , q= +Ze
Current constituted , I = e/T       .... (1)
where, T is the time period of revolution.

Let, r be the orbital radius of the electron.
v be the orbital speed. 
Then,
                 T= 2πrv.

Putting this equation in (1) we get, 
 
                     I=ev2πr 
Magnetic moment is given by, 
       μ = IA = I×πr2    =ev2πr× πr2    = evr2