Question

The deflecting torque acting on the coil of galvanometer is:

a)inversely proportional to number of turns.

b) inversely proportional to current flowing.

c)inversely proportional to area of coil.

d) directly proportional to the magnetic field strength​

Answer 1

The deflecting torque acting on the coil of galvanometer is:

• directly proportional to the magnetic field strength

But how?

• We know that in a galvanometer, the striker is placed in a radial magnetic field such that the torque experienced will be:

$\vec{\tau }= \vec{M} \times \vec{B}$

$\implies | \vec{\tau } | = M \times B \times \sin( \theta)$

• For radial fields, we can say:

$\implies | \vec{\tau } | = M \times B \times \sin( {90}^{ \circ} )$

$\implies | \vec{\tau } | = M \times B$

$\implies | \vec{\tau } | = ( i \times area) \times B$

For constant current and area:

$\implies | \vec{\tau } | \propto B$

So, the torque is directly proportional to magnetic field intensity.