Since the motor has a radial magnetic field, it means that at whatever angle the armature is at, torque would be max right???? Therefore the answer should be B???? Can anyone explain why the answer according to the sample answer is D??
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- Thread starter phewsz
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The torque decreases as the motor picks up speed (angular velocity) because the back emf builds up as the motor picks up speed (as time goes on). The back emf builds up, so net current flowing through the coil decreases, leading to lower torque, since 
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Basically the magnets are curved so that the field lines are perpendicular to the plane of the motor's coil at all times, so that the force experienced by the wire is always maximal (in the sense that the angle between the plane and the field is always 90 degrees). See this image: http://www.google.com.au/imgres?img...d=0CB0QMygBMAFqFQoTCMLTy4TWhMcCFcMYpgod1jcOJg
drainbammage
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Which way should you draw radial field lines? Ive been both in past paper answers.
http://puu.sh/jk43H/878abf011e.jpg
It shouldn't matter, especially as past paper answers have both you say (assuming these were official HSC papers). Just copy what's done in a reputable HSC Physics textbook (e.g. the one published by Jacaranda).
mrpotatoed
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I thought the one where they cross is wrong? The spacing between the lines is used to show the strength of the field... field lines can't cross because that implies an infinite intensity at that spot which is of course impossible, right?
