Answer:
Step-by-step explanation:
Let the earth's magnetic field be H at that location .
Iniially the axis of coil is aligned with magnetic field so magnetic field must be perpendicular to face of the coil.
Initial magnetic flux passing through the coil
= n B A , n is number of coils , B is magnetic field and A is area of the face of the coil .
= 664 x B x π r²
= 664 x B x 3.14 x 9 x 9 x 10⁻⁴
= 16.89 B Weber
When the coil is turned so that its face becomes parallel to the magnetic field , flux passing through it becomes zero.
change in flux = 16.89B - 0
= 16.89 B
time = 3.5 x 10⁻³ s
induced voltage = change in flux / time
= 16.89 B / 3.5 x 10⁻³
.16 = 16.89 B / 3.5 x 10⁻³
B = .16 x 3.5 x 10⁻³ / 16.89
= .033155 x 10⁻³
3.3155 x 10⁻⁵ t
33.155 x 10⁻⁶
= 33.155 µT.