Exploring Induced EMF: Polarity and Direction of a Bicycle Wheel Experiment

[ehabmozart]

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!

 

[ehabmozart]

Guys! I urgently need help. Thanks!

 

[ehabmozart]

People Here! This is one important question... Please help whoever can contribute with a good reply... I will owe him/her big time!

 

[dikmikkel]

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.

 

[Nickie]

I would first clarify the variables and conditions of the experiment before proceeding with a solution. It is important to note the orientation of the wheel and the direction of the Earth's magnetic field. Based on the given information, the wheel is spinning clockwise and the Earth's magnetic field is acting into and perpendicular to the paper.

Using Lenz's Law, we know that the induced EMF will try to oppose the change in magnetic flux. In this case, the magnetic field is increasing as the wheel spins, so the induced EMF will be in the opposite direction, or counterclockwise. This means that the polarity of the EMF will be negative at the hub and positive at the rim.

To determine the direction of the spokes, we can use Fleming's right hand rule. If we point our right thumb in the direction of the motion (clockwise), our fingers will curl in the direction of the induced EMF (counterclockwise). This means that the spokes will be pointing towards the center of the wheel.

Overall, the induced EMF will be negative at the hub and positive at the rim, and the spokes will be pointing towards the center of the wheel. This experiment demonstrates the concept of induced EMF and the relationship between magnetic fields and motion.