Answer:
a) for the torque to be maximum, sin should be maximum
i.e (sinФ)maximum = 1
b) therefore the Maximum torque is
Tmax = 0.1838 Ć 1 = 0.1838 Ā N.m
c) Given the torque is 71.0% of its maximum value; Ф Ā = 45.24ā° ā 45ā°
Explanation:
Given that; Diameter is 8.40 cm,
Radius (R) = D/2 = 8.40/2 = 4.20 cm = 0.042 m
Number of turns (N) = 17
Current in the loop (I) = 3.20 A
Magnetic field (B) = 0.610 T
Let the angle between the loop's area vector A and the magnetic field B be
Now. the area of the loop is;
A = ĻR²
A = 3.14 ( 0.042 )²
A =  0.005539 m²
Torque on the loop (t) = NIABsinФ
t = 17 Ć 3.20 Ć0.005539 Ć 0.610 Ć sinФ
t = 0.1838sinФ N.m
for the torque to be maximum, sin should be maximum
i.e (sinФ)maximum = 1
therefore the Maximum torque is
Tmax = 0.1838 Ć 1 = 0.1838 Ā N.m
Given the torque is 71.0% of its maximum value
t = 0.71 Ć tmax
t = 0.71 Ć 0.1838
t = 0.1305
Now
0.1305 N.m =  0.1838 sinФ N.m
sinФ = 0.1305 / 0.1838
sinФ = 0.71001
Ф = sinā»Ā¹ 0.71001
Ф Ā = 45.24ā° ā 45ā°