1.

The magnetic field at the centre of a circular coil of radius r is pi time that due to a long straight wire at a distance r from it for equal currents. The following figure show three cases. In all cases the circular part has radius r and straight ones are infinitely long. For same current, the B field at the centre P in cases 1, 2, 3, has the ratio

Answer»

`(-(PI)/(2)):((pi)/(2)):((3pi)/(4)-(1)/(2))`
`(-(pi)/(2)+1):((pi)/(2)+1):((3pi)/(4)+(1)/(2))`
`-(pi)/(2):(pi)/(2):3(pi)/(4)`
`(-(pi)/(2)-1):((pi)/(1)-(1)/(4)):((3pi)/(4)+(1)/(2))`

Answer :A


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