Q.

An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current 'I' along the same direction as shown in figure. Magnitude of force per unit length on the middle wire B is given by              [2017]


 

1 2μ0I2πd  
2 2μ0I2πd  
3 μ0I22πd  
4 μ0I22πd  

Ans.

(3)

Force between wires A and B = force between wires B and C

  FBC=FAB=μ0I2l2πd

As,  FABFBC net force on wire B,

Fnet=2FBC=2μ0I2l2πd

or  Fnetl=μ0I22πd