Deflecting Torque for Moving-Coil Instrument

Deflecting Torque for Moving-Coil Instrument Points : Deflecting Torque for Moving-Coil Instrument When current is passed through the coil, force acts upon its both sides which produces a deflecting torque.
Let B = Flux density in Wb/m² (Tesla)
λ = Length or depth of the coil in meter
b= Breadth of coil in meter
N= Number of turns in the coil
If I ampere is the current passing through the coil, then the magnitude of the force experienced by each of its sides is = BIλ Newtons.
For N turns, the force on each side of the coil is = NBIλ Newtons.
= Force x perpendicular distance
=NBI (λxb)
=NBI (λxb)
= NBIA Newton meter
when A is the face area of the coil.
It is seen that if B is constant, then λ_d is proportional to the current passing through the coil.