Question

Deflection magnetometer is held in $\tan B$ position. A magnet placed on one of its arms produces no deflection. This implies that the axis of the magnet is

• A. in the east - west direction
• B. in the north-south direction
• C. perpendicular to the wooden bench
• D. North - East

Answer 1

The correct option is B in the north-south direction

In $\tan B$ position , the arms are in the north south direction and the aluminium pointer are in east- west direction. So the compass needle is in north- south direction. For the magnetic field lines of the magnet to be ineffective then they must be in the north south direction so that they will not create a torque.
If the magnet is in east- west direction , a couple acts on the magnet and thus causes deflection.