Question

A tangent galvanometer of reduction factor $1A$ is placed with a plane of its coil perpendicular to the magnetic meridian when a current of $1A$ is passed through it. The deflection produced is
$A)\text{ }{{45}^{0}}$
$B)\text{ }{{\text{0}}^{0}}$
$C)\text{ 3}{{\text{0}}^{0}}$
$D)\text{ 6}{{\text{0}}^{0}}$

Answer 1

Hint: This problem can be solved by recalling that a tangent galvanometer must be placed along the magnetic meridian so that a deflection can be produced due to the action of two mutually perpendicular fields. However, in this case the galvanometer is placed perpendicular to the magnetic meridian.

Complete step-by-step answer: A tangent galvanometer produces a deflection when two mutually perpendicular magnetic fields act on it, one of which usually is the horizontal component of the earth’s magnetic field at that point.
Due to this reason, a tangent galvanometer is placed along the magnetic meridian, so that the horizontal component of the earth’s magnetic field and a magnetic field produced by the current carrying coil inside the galvanometer are in mutually perpendicular directions.
If the galvanometer is placed perpendicular to the magnetic meridian, the horizontal component of the magnetic field and the magnetic field produced by the current carrying coil will be in the same direction and hence, their resultant will also be in the same direction, thus giving zero deflection in the tangent galvanometer.
Hence, in this case the deflection in the tangent galvanometer will be zero.
Therefore, the correct option is $B)\text{ }{{\text{0}}^{0}}$.

Note: The reduction current of a tangent galvanometer is the current that produces a deflection of ${{45}^{0}}$ when placed properly in the magnetic meridian. However, since in this question the tangent galvanometer has not been placed correctly along the magnetic meridian, the reduction factor does not come into the question at all. It is given to confuse the students and to check whether they know the concept of the proper alignment of a tangent galvanometer or not.