A solenoid 60 cm long and of radius 7.0 cm has 3 layers of windings of 300 turns each. A 2.0 cm long wire of mass 2.5 g lies inside the solenoid (near its centre) normal to its axis, both the wire and the ais of the solenoid are in the hoorizontal plane. The wire is connected through two lead parallel to the axis of the solenoid to an external battery which supplies a current of 6.0 A in the wire. What value of current (with appropriate sense of circulation) in the windings of the solenoid can support the weight of the wire ? `g=9.8 m s^(-2)`.

Explanation

`B=mu_(0)n I`
Force acts on the wire normal to its length
`therefore F= BI^(1)l`
`=mu_(0)n II^(1)l and n=((900)/(60))/(100)=1500`
`=mu_(0)n II^(1)l = mg`
`I=(2.5xx9.8)/(1000xx4pixx10^(-7)xx1500xx6xx(1)/(15))=108 A.`