Question

There is no couple acting when two bar magnets are placed co-axially separated by a distance because :

• A. there are no forces on the poles
• B. the forces are parallel and their lines of action do not cincide
• C. the forces are perpendicular to each other
• D. the forces act along the same line

Answer 1

The correct option is D the forces act along the same line

$\overrightarrow{\tau }=\overrightarrow{M}\times \overrightarrow{B}=0$
$MB\sin \theta =0$
$\sin \theta =0$
$\Rightarrow \theta =0$
$\Rightarrow$ Magnetic field lines of both the magnets are in the same line which results in forces due to both magnets act along the same line