The full-scale deflecting torque is Td = NBIA N-m
where I is the full-scale deflection current ;
I = 5mA = 0.005A
Td = 100 × B × 0.005 × (3 × 2.5 × 10−4 ) = 3.75 × 10−4 B N-m
The controlling torque is
Tc = 0.5 g-cm = 0.5 g. wt.cm
= 0.5 × 10−3 × 10−2 kg wt-m
= 0.5 × 10−5 × 9.8
= 4.9 × 10−5 N-m
For equilibrium, the two torques are equal and opposite.
∴ 4.9 × 10−5 = 3.75 × 10−4 B
∴ B = 0.13 Wb/m2