The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?

Given:


Current through the wire, I = 300 A


Length of wire, L1 = 70 cm


Length of wire, L2 = 70 cm


Distance between the wires, d = 1.5 cm



We understand that current carrying conductors create magnetic fields which in turn applies force on nearby current carrying conductor(s).


We know that,


…(1)


Where,


F = force applied


�0 = permeability of free space


I = current through the conductors


d = separation between the conductors


Now, putting the values of F, �0, I and d in equation (1)


⇒


⇒ F = 1.2 Nm-1


Hence, the force applied on the wires is 1.2 N per metre. The force is repulsive in nature because the current is carried in the opposite direction.


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