How Does Induced EMF Affect the Polarity of a Spinning Bicycle Wheel?

AI Thread Summary
Induced electromotive force (EMF) occurs across the spokes of a spinning bicycle wheel due to the interaction with Earth's magnetic field, which is horizontal and perpendicular to the wheel's plane. The polarity of the hub and rim can be determined using Faraday's law, which states that a change in magnetic flux induces a current. Lenz's law indicates that the induced EMF will oppose the change in magnetic flux, providing insight into the direction of the induced current. The discussion emphasizes the need to apply the right-hand rule to ascertain the direction of motion and the resulting EMF. Understanding these principles is crucial for solving the problem effectively.
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Homework Statement


A student is experimenting with a bicycle wheel. He turns the bicycle upside down and spins the wheel in a vertical plane at a constant rate. The diagram shows the wheel. At the place where the experiment is performed, the Earth‟s magnetic field is in a horizontal direction. It acts into and perpendicular to the paper.

A constant e.m.f. is induced across the length of each spoke.
(i) Label the hub and rim either plus or minus to show the polarity of the e.m.f.

The figure shows a wheel with the direction of motion clockwise. The hub is the center and the rim are the outerpart


Homework Equations


Lenz's Law


The Attempt at a Solution


Well, in this problem, it is said that the magnetic field lines point inside the paper. So if this is cut, it tries to oppose it... Hence, magnetic field lines should be outside. We should use flemings right hand rule but i have no idea about what would be the new direction of the spokes of the wheel (i.e the motion) and indeed upon that i don't know the direction of E.M.F... I need help urgently.. Thanks!
 
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You didn't post the diagram.
Lentz's law isn't the appropriate one. You need to use Faradays law: "change in magnetic flux induces a current"(tries to oppose the change in magnetic flux according to lenz law)
So it induces an EMF which should result in an opposing magnetic flux.
So Lenz's law only gives a hint of the direction.
 

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