Correct Answer - Option 2 : 11.11 mA
Concept:
PMMC torque equation
Td = Tc
Td = deflecting torque
Td = BINA
where B = flux density
I = current in moving coil
N = number of turns of the coil
A = effective Area of coil
Tc = controlling torque
Tc = Kθ
K = spring constant
θ = deflection Angle.
Kθ = BINA
Calculation:
Given:
θ = 100°, N = 60, B = 0.5T, l = 25mm, W = 18 mm
Area (A) = l × W = 25 × 18 = 450 mm2 = 450 × 10-6 m2
K = 1.5 × 10-6 N-m/degree
By torque equation
Kθ = BINA
1.5 × 10-6 × 100 = 0.5 × I × 60 × 450 × 10-6
I = 11.11 mA