Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the
Magnetic force on the 20-A wire has magnitude F, what is the magnitude of the magnetic force on
The 5-A wire? No external magnetic fields are present.
A) $F / 4$
B) $4 F$
C) $F / 2$
D) $F$
E) $2 F$

Question

Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the
Magnetic force on the 20-A wire has magnitude F, what is the magnitude of the magnetic force on
The 5-A wire? No external magnetic fields are present. 
A) $F / 4$
B) $4 F$
C) $F / 2$
D) $F$
E) $2 F$

Quizplus · Accepted Answer

The magnetic force between two parallel currents is equal for both wires due to Newton's third law (action and reaction forces are equal and opposite). Thus, the magnitude of the force on the 5-A wire is the same as the force on the 20-A wire, regardless of the difference in current magnitude.

Two Long Parallel Wires Are Placed Side-By-Side on a Horizontal F/4F / 4F/4

Two Long Parallel Wires Are Placed Side-By-Side on a Horizontal $F / 4$