To solve this problem we apply the concepts related to the electric torque generated by the electromagnetic field. Mathematically this Torque can be written under the following relation
[tex]\tau = NIAB sin\theta[/tex]
Here,
N = Number of Turns
I = Current
A = Area
B = Magnetic Field
The maximum torque will be reached when the angle is 90 degrees, then we will have the following relation,
[tex]\theta = 90\°C[/tex]
Magnetic Field is given at function of the number of loops, permeability constant at free space at the perimeter, then
[tex]B = \frac{N\mu_0 I}{2\pi r}[/tex]
[tex]B = \frac{(60)(4\pi * 10^{-7})(4.2)}{2\pi (0.1)}[/tex]
[tex]B = 5.04*10^{-4}T[/tex]
Replacing at the first equation we have,
[tex]T = (20)(\pi (0.005)^2)(1)(5.04*10^{-4})[/tex]
[tex]T = 7.91*10^{-7}N\cdot m[/tex]
