Explain question no.40. Ans is(1):

40. Figure shows a circular wheel of radius 10.0 cm whose upper half is made of iron and lower half of wood. The two junctions are joined by an iron rod. Uniform magnetic field B of magnitude 2x10^-4 T exists in space as shown. The wheel is set in pure rolling. If it takes 2.0 s for the iron part to come down and wooden part to go up then average induced emf during this period is. 

(1) 1.57 x 10^-6V        (2) 1.5 x 10^-7 V
(3) 15.7 x 10^-6 V        (4) 1.55 x 10^-8 V