8

9-6. A 100-turn coil of circular cross section is wound compactly so that all loops lie in approximately the same plane. The average radius of the coil is 3 cm. The coil rotates about one of its diameters at 900 rev/min. When the rotation axis is vertical, the average induced emf in the coil is found to be 0.50 mv. What can be concluded about the earth's magnetic field at the location of the coil