# Find the power required to pull loop through constant magnetic field

## Homework Statement

The wire shown is being pulled through a constant magnetic field of 0.25 Tesla at 3 m/s.

A) Find the power required to pull the loop at this speed.
B) If the wire has a resistance of 100 ohms, what is the current in the wire?

## The Attempt at a Solution

I am trying to teach myself this problem, as I missed a week of school because of a back surgery and the slides I was given are wholly inadequate. I am not looking for a simple solution, but an explanation and a little bit of guidance to point me in the right direction would be stupendous.

This isn't a homework problem (as in it has a due date) but it is in the back of the book and is listed as difficult.

The picture (I have drawn) is here: http://twitpic.com/7e6nad [Broken]

Thank you all.

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Consider the loop consisting of atoms.Each atom has electron's and in metals these electrons are free to move.Due to action of magnetic field we have force on electron as e*(v x B). Here 'x' is cross product of vectors.So electrons move to one end and all protons remain where there are.Thus creating a potential difference and causing a current.And yes power is force is= Force*Velocity=e*(v x B) * v=e*(v^2)*B.
Value of potential Difference=B*l*v
Where l is length of rod.It must be given.
Otherwise use power I^2*R(resistance)=F*v.
Get current.
B is magnetic field and v is velocity of electron and e is charge on electron.

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Power = force x velocity.
Do you know how to calculate the force on the wire in the magnetic field?

what is the force acting on the wire due to the magnetic field?

q(vxB)=F since there is no electric field.

and current is dq/dt which you could say is qv, but i think power is I2R = P

Power is F*v=P

Power = force x velocity.
Do you know how to calculate the force on the wire in the magnetic field?
Isn't it F=BILsinθ? But surely that doesn't apply here? There is no length given, after all.

For B) If the wire has a resistance of 100 ohms, what is the current in the wire? I=V/R, but I do not know the voltage, nor am I certain how I can ascertain it with the given information.

I feel that I may have jumped ahead of the class with this problem, but I really want to grasp the material.

Consider the loop consisting of atoms.Each atom has electron's and in metals these electrons are free to move.Due to action of magnetic field we have force on electron as e*(v x B). Here 'x' is cross product of vectors.So electrons move to one end and all protons remain where there are.Thus creating a potential difference and causing a current.And yes power is force is= Force*Velocity=e*(v x B) * v=e*(v^2)*B.
Value of potential Difference=B*l*v
Where l is length of rod.It must be given.
Otherwise use power I^2*R(resistance)=F*v.
Get current.
B is magnetic field and v is velocity of electron and e is charge on electron.
Length of rod is not given. Truly.

e*(v^2)*B would be 3.6E-19 N?

I^2*r=F*v => I = 1.04E-10 amps? Does that seem correct?

If you have(Covenant32) calculated correctly then it might be.Method remains as stated.All rest is calculation.