1.

A long straight wire in the horizontal plane carries as curret of 75 A in north to south direction, magnitude and direction of field B at a point 3 m east of the wire isA. `4xx10^(-6)T`, vertical upB. `5xx10^(-6)T`, vertical downC. `5xx10^(-6)T`, vertical upD. `4xx10^(-6)T`, vertical down

Answer» Correct Answer - C
From Ampere circuital law
`ointvecB.vec(dl)=mu_(0)I_("enc")`
`Bxx2piR=mu_(0)I_("enc")`
`B=(mu_(0)I_("enc"))/(2piR)=2xx10^(-7)xx(75)/(3)=5xx10^(-6)T`
The direction of field at the given point will be vertical up determined by the screw rule or right hand rule.


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