Calculating Magnetic Field to Overcome Friction in Metal Wire Setup

[Dr.Brain]

Ok there are two plastic rails over which a metal wire is kept , the wire is kept prependicular to both plastic rails , over the rails.. The coefficient of friction is 'n' between the metal and the plastic . The mass of the plastic wire is 'm' , Calculate the magnitude of the Magnetic field B , which just allows the wire to move.

I equate dthe net frictional force which will try to limit the motion , with the Magnetic force given by ILB , but in the answer instead of 'n' . there is some square root fuction of 'n'in the denominator and n in the numerator. , please help.

 

[Chi Meson]

The wire will feel no force at all unles there is a current going through it. What information do you have about the current in this wire? I'm assuming this is not a magnetic wire (not iron or cobalt)?

 

[Dr.Brain]

ok the current in the wire is 'i' .

 

[Chi Meson]

I assume there is also an "L" given. In that case you are exactly right. B=('n'mg)/(IL)

 

[Dr.Brain]

but the answer is given to be : nmg / (IL)[sqrt(1+n(^2)]

 

[Chi Meson]

What level of physics is this? High school or college, and is it calculus based? Are you using differential equations?

I can not think of any reason why increasing the coefficient of friction should decrease the required magnetic field to start moving an object by the lorentz force. This is either an advanced, peculiar property I don't know about, or a mistake.

ANyone else want this one?

 

[Dr.Brain]

I am in my first year at a tech-school , and this is Physics-II which we r taught in the second semester , but I think it doesn't matter what level i am studing , i just need to solve the problem. Use calculus or whatever .

 

[Chi Meson]

I've looked in six college textbooks, and I can't find any reference to that peculiar formula. Sorry, but I'm done here