Given that, for a moving coil galvanometer, Effective area, A=4×10−2m2 Magnetic field, B=5×10−2‌Wb‌m−2 Angle of deflection, ϕ=0.2‌rad Electric current, l=5‌mA=5×10−3A By using the relation, NABI=Cϕ [where, C = torsional constant] ⇒C=