A long, straight wire of negligible mass is placed in a region that contains a…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Magnetism and Electromagnetism · Magnetism and Electromagnetism
Problem
A long, straight wire of negligible mass is placed in a region that contains a uniform magnetic field of magnitude B0. The wire can be rotated about its midpoint so that the angle θ between the direction of the conventional current I (along the length of the wire) and the magnetic field can be varied from 0∘ to 90∘. The length of the portion of the wire that is inside the magnetic field is fixed at ℓ.
(a) Describe qualitatively how the magnitude of the magnetic force on the wire depends on the angle θ. In your description identify the value(s) of θ for which the force is (i) maximum, (ii) zero, and (iii) one–half of its maximum possible value, and explain your reasoning in each case without using a written mathematical formula.
(b) As the wire is slowly rotated from θ=0∘ to θ=90∘, a student claims that the component of the force parallel to the wire causes the charge carriers to accelerate along the wire. Evaluate this claim and justify your answer based on the orientation of the magnetic field relative to the current.
(c) Suppose the magnetic field were instead re-oriented so that it always remained perpendicular to the plane in which the wire is being rotated. Explain whether any value of θ would now result in zero magnetic force on the wire. Support your answer with a clear conceptual argument.