Physics help The homopolar generator, also called the Faraday disk, is a low-vol
ID: 1381049 • Letter: P
Question
Physics help The homopolar generator, also called the Faraday disk, is a low-voltage, high current electric generator. It consists of a rotating conducting disk with one stationary brush (a sliding electrical contact) at its axle and another at a point on its circumference as shown in the figure below. A uniform magnetic field is applied perpendicular to the plane of the disk. Assume the field is 0.900 T, the angular speed is 3.72 Times 10 3 rev / min, and the radius of the disk is 0.460 m. Find the emf generated between the brushes, when superconducting coils are used to produce a large magnetic field, a homopolar generator can have a power output of several megawatts. Such as generator is useful, for example in purifying metals by electrolysis. If a voltage is applied to the output terminals of the greater, it runs in reverse as a homopolar motor capable of providing great torque useful in ship propulsion.
Explanation / Answer
angular speed (w) = angle (@) / time ( during one revolution @ = 2*pie)
w = 3.72*103 *2*3.14 / 60 ( @ = 3.72*103 *2*pie) , ( 1 min = 60 sec)
w = 389.36 rad/sec
When a disc of radius r rotates with a uniform angular speed w in a perpendicular magnetic field B, The emf induced between the axis of disc and its rim ( ie in the brushes here) is:
e = (1/2) * B*w*r2
e = (1/2) * 0.900*389.36*( 0.460)2
e = 37.07 volt