Question

Three wires $A,B$, and $C$ all are all parallel and have the same magnitude of current. Wires $A$ and $B$ have current going toward the top of the screen while wire $C$ has current going toward the bottom of the screen.
What is the direction of the force on $A$ because of the other two wires?

• A. To the right.
• B. To the left.
• C. Into the screen.
• D. Out of the screen.

Answer 1

The correct option is A To the right.

From Fleming's Right Hand thumb rule, the magnetic field acting on wire A due to wire B is out of the page, whereas due to C is into the page. Now the magnetic field due to a current carrying wire decreases with increasing distance from the wire. Hence magnetic field at A due to C is weaker than that due to B. Therefore net magnetic field acts out of the page at A.
From $\overrightarrow{F}=I(\overrightarrow{l}\times \overrightarrow{B})$, the net force acts to the right.