840_Physics ProblemsTechnical Physics

# 840_Physics ProblemsTechnical Physics - 180 P29.62 Magnetic...

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180 Magnetic Fields P29.62 Suppose the input power is 120 120 W V = af I : I ~1 10 0 A A = . Suppose ω π = F H G I K J F H G I K J 2000 12 200 rev min min 60 s rad 1 rev rad s ~ and the output power is 20 200 r a d s == τω τ bg ~10 1 Nm . Suppose the area is about 34 cm cm × ,o r A 3 m 2 . Suppose that the field is B 1 T . Then, the number of turns in the coil may be found from NIAB : 01 1 31 .~ Nm Cs m NsCm 2 ⋅⋅ −− N ej e j giving N 3 . *P29.63 The sphere is in translational equilibrium, thus fM g s −= sin θ 0. (1) The sphere is in rotational equilibrium. If torques are taken about the center of the sphere, the magnetic field produces a clockwise torque of magnitude µθ B sin , and the frictional force a counterclockwise torque of magnitude fR s , where R is the radius of the sphere. Thus: B s sin (2) From (1): g s = sin . Substituting this in (2) and canceling out sin , one obtains µ BM g R = . (3) I f s B Mg µ G G FIG. P29.63 Now µπ = NI R 2 . Thus (3) gives I Mg NBR = ππ 008 980 503 5 0 02 0713 .. . kg m s T m A 2 a fa fa f
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## This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .

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