1. The problem statement, all variables and given/known data A copper disc of radius 10 cm is situated in a uniform field of magnetic flux density 1.0 * 10-2 T with its plane perpendicular to the field. The disc is rotated about an axis through its centre parallel to the field at 3.0 * 103 rev min-1. Calculate the EMF between the rim and centre of the disc. Answer: 16 mV. 2. The attempt at a solution Attempt 1 E = B A N ω, where ω = 2 π / T, where T = 1 / f. f = 103 rev min-1 / 60 = 16.7 rev s-1. ω = 2 π / 16.7 = 104.9 rad s-1. E = 10-2 * (0.1 * 0.1) * 104.9 = 0.01049 V. Attempt 2 I also used another formula: E = f B π (r22 - r12) where r2 = radius of rim, r1 = radius of axle. E = 16.7 * 10-2 * π * 0.12 = 5.2 * 10-3 V. What am I missing?