Question

Two parallel wires carrying currents in the same direction attract each other because of

• A. potential difference between them
• B. mutual inductance between them
• C. electric force between them
• D. magnetic force between them

Answer 1

Answer: (D)

As shown in the figure, let the conductor $Y$ carry current $i_{2}$, situated in a magnetic field perpendicular to its length. It therefore, experiences a magnetic force, the magnitude of the force acting on a length $l$ of $Y$ is
$F=i_{2} B l=i_{2}\left(\frac{\mu_{0}}{2 \pi} \frac{i_{2}}{R}\right) l$
From Fleming's left hand rule the direction of this force is towards $X$. Similarly, force per unit length of $X$ due to $Y$ is directed opposite to $Y$. Hence, the conductors attract each other.