Physics Magnetism help.......

[Koing]

I am having problems with this questions:

A wire of superconducting niobium of radius 0.100cm can carry a current of 1500 A. The denisty of niobium is 8600kgm^-3. what field must the wire be placed in so that it levitates, that is, it floats with no visible means of support? (The length of wire is not needed so solve the problem.)

I have the answer but I can't work how to get it? Anyone know and can show me?

 

[GoodToGo]

Equate magnetism generated from an infinite wire to the weight of the wire.

 

[Koing]

<< Equate magnetism generated from an infinite wire to the weight of the wire. >>



WTF? How am I going to equate magnetism generated from an infinite wire to the weight of the wire FROM the EXACT question that is given to me?

A wire of superconducting niobium of radius 0.100cm can carry a current of 1500 A. The denisty of niobium is 8600kgm^-3. what field must the wire be placed in so that it levitates, that is, it floats with no visible means of support? (The length of wire is not needed so solve the problem.)

To work out the weight of the wire I would need the density which I have. The *LENGTH* which I do not have and do not need as the question states that I don't need it. Please read the question before helping.

 

[GoodToGo]

Whats the formula for the force generated from a wire placed in a magnetic field?

 

[Koing]

these are the forumlas I know

F = BIL

therefore

B = F/IL

and I can get F by F = mg

I just can't work it out to get the answer. I knew I had to equate the magnetism of the wire to the weight of it to make it levitate but HOW is what I'm asking for.

 

[GoodToGo]

F=Bil=mg where m= mass, g=gravity

mass=volume*density
volume=l*pi*r^2

Therefore Bil=m*g=l*pi*r^2*rho*g
The lengths CANCEL from both sides.
Bi=pi*r^2*rho*g

Now what do u say?

 

[Koing]

I say thank you very much!