Electromagnetic Induction

If a wheel with 24 metallic spokes each 40 cm long is rotated with a speed of 180‌rev∕min in a plane normal to the horizontal component of earth's magnetic field, the emf induced between the axle and the rim of the wheel is E . If the number of spokes is made 12 and the wheel is rotated with a speed of 90‌rev∕min in the same field, the induced emf is