A wheel with 20 metallic spokes each 1 m long is rotated with a speed of 120 rpm in a plane perpendicular to a magnetic field of 0.4 G. The induced emf between the axle and rim of the wheel will be (1 G = 10–4 T)
(1) 2.51 V
(2) 2.51 × 10–4 V
(3) 2.51 × 10–5 V
(4) 4.0 × 10–5 V