Two long parallel conductors are carrying currents in the same direction as shown in the figure. The upper conductor `A` carrying a current of `100 A` is held firmly in position. The lower conductor `B` carries a current of `50 A` and free to move up and down. The linear mass density of the lower conductor is 0.01 kg/m.

Options

A. conductor B will be in equilibrium if the distance between the conductors is `0.1 m`
B. Equilibrium of coductor B is unstable
C. both a and b are wrong
D. both a and b are correct

Answer

D

Explanation

`F/l=weight` per unit length
`:.mu_0/(2pi) (i_1i_2)/r=0.01xx10`
or `((2xx10^I=-7)(100xx50))/r=0.01`
or `r=0.1m`,
We `B` wire is displaced downwards from equilibrium positon, magnetic attraction form `A` wire will decrease (which is upwards) But, weight (which is downwards), So net force is downwards, in the direction of displacment frm themean position or away from the mean position. Hence, equilibrium in unstable