Question
8 marksAnswer all parts using electromagnetic induction and energy transfer. No numerical calculation is required.
1(a)
A classroom model of regenerative braking has a flywheel connected to a coil rotating in a uniform magnetic field. The angle between the coil's normal and the field changes as it rotates. Slip rings and brushes connect the coil to a fixed resistor in a complete circuit.
Explain why the rotating coil produces a current in the resistor. Use magnetic flux linkage in your answer.
[3 marks]
1(b)
The flywheel is given an initial spin and then left to turn the generator without any further push. Ignore friction in the bearings. The resistor remains connected.
Use Lenz's law and energy conservation to explain why the flywheel slows down and where its decreasing kinetic energy goes in this model.
[3 marks]
1(c)
The circuit is opened, while the coil continues to rotate. Compare the induced emf and the energy delivered electrically to the external resistor with the connected case at the same instantaneous rotational speed and orientation.
Assume an ideal generator with the same magnetic field and ignore eddy currents and mechanical losses.
[2 marks]
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