A heavy aluminium disc has a radius of 
. The disc rotates with the wheels of a vehicle and forms part of an electromagnetic braking system on the vehicle. In order to activate the braking system, a uniform magnetic field of flux density 
is switched on. This magnetic field is perpendicular to the plane of rotation of the disc, as shown in the figure below.
Define magnetic flux.
Calculate the magnetic flux through the disc. Give a unit with your answer.
The disc is rotating at a rate of 25 revolutions per second. Calculate the magnitude of the electromotive force (e.m.f.) induced between the axle and the rim of the disc.
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