Question

A magnetic compass needle is placed on the plane of paper near point A in which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the the deflection of the magnetic compass. When is the deflection maximum?
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Answer 1

The deflection will be maximum when the magnetic field due to the compass is perpendicular to the direction of the current. So, if we place the conductor on the plane of the paper the deflection of the compass will be minimum.
On, the other hand if the current carrying conductor is perpendicular to the magnetic field, the deflection of the magnetic field will be maximum.
OR
We know that when the magnetic field and the direction of current are perpendicular to each other, the deflection is maximum. But when they are in the same plane, no deflection takes place. So, the current carrying conductor needs to be placed in the same plane as the magnetic compass to attain no deflection.