1.

A star shaped loop ( with `l=` length of each section ) carries current i. Magnetic field at the centroid of the loop is A. `(3mu_(0)i)/(pi l)`B. `(3 mu_(0)i)/(2pi l)`C. `(3-sqrt(3))(mu_(0)i)/(pil)`D. `(3+sqrt(3))(mu_(0)i)/(pil)`

Answer» Correct Answer - C
`r=(sqrt(3)l)/(2)`
`B=6[(mu_(0))/(4pi)(i)/(r)(sin 60^(@)+sin60^(@))]`
`-6[(mu_(0))/(4pi).(i)/(r)(sin30^(@)+sin30^(@))]`
`=6xx(mu_(0))/(4pi).(i)/(r)(sqrt(3)-1)`
`=6xx(mu_(0))/(4pi).(i)/(((sqrt(3)l)/(2)))(sqrt(3)-1)`
`=(3-sqrt(3))[(mu_(0)i)/(pi l)]`


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