Question
Two long current carrying thin wires, both with current I, are held by insulating threads of length L and are in equilibrium as shown in the figure, with threads making an angle ‘θ’ with the vertical. If wires have mass λ per unit length then the value of I is: (g = gravitational acceleration)
Solution
B.
consider free body diagram of the wire
As the wires are in equilibrium. they must carry current in opposite direction.
Here, 
, where l is the length of each wire are d is a separation between wires.
From the diagram, d = 2L sin θ
T = cos θ = mg = λlg
(in vertical direction) ..... (i)
(In horizontal direction) ..... (ii)
From eqs. (i) and (ii)
