Home > Science Group > Question and Answer

Science Group

Question:

starshippiy
starshippiy
Student
College - Freshman

A coil made of wire of copper, with wire's diameter d, traversed by a current I, is coaxial set into a magnetic field.

At what magnetic induction the coil is breaking?

The copper breaking stress is sigma=280MN/m^2 and radius of coil, R.

Rate question:

Posted by starshippiy on Saturday July 4, 2009 at 6:29 AM and tagged with magnetic induction, science, wire of copper.

Answers:

  1. giorgiana1976
    giorgiana1976 Teacher
    Doctorate

    eNotes Editor

    We'll consider a spiral element, which comprises a central angle dt. The electromagnetic force is acting on the element, dF=l*ds*B; also the stresses T, from the bottoms, are acting on the element. The resultant of both stresses is centripetal:

    2*T*sin(dt/2)=2*T*(dt/2)=T*dt , ( (sindx)/dx=1)

    The resultant is balancing the force dF, which is centrifugal:

    dF=l*ds*B=T*dt, T=l*ds*B/dt=I*B*R

    On the other hand,T=sigma*S=sigma*(pi*d^2/4)

    so that, B=T/(I*R)=(pi*d^2/4)*sigma/(I*R)

    The usual magnetic fields are B<10T

    Rate answer:

    Posted by giorgiana1976 on Wednesday July 8, 2009 at 11:14 AM