Posted by **Alfred** on Monday, August 31, 2009 at 6:00am.

A dc electric motor found in the lab was being examined by a student. It was connected to a power supply and it was not attached to any load.

(a) The student stated, ‘when the motor is switched on, the electrical energy input should cause the motor to start rotating, and the rotation rate should increase without limit since there is no load.’ Asses the validity of this statement, mentioning the principles involved.

(b) Calculate the current flowing in a motor having 210 turns of coil in the armature, which is a 3.0 x 3.0 cm square coil within a magnetic field of 0.023 T, when it is providing a maximum torque of 2.7 x 10-2 Nm.

(c) For the motor used in part (b), calculate the angle the coil is making with the magnetic field when the torque is only one half of its minimum value.

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