A straight wire of length carrying current is placed in a uniform magnetic field of…
MATHEMATICS · Multi-part · A Level · Mathematics · Forces and Newton's laws · Forces and Newton's laws
Problem
A straight wire of length L carrying current I is placed in a uniform magnetic field of strength B. Initially the wire makes an angle of 60∘ with the direction of the magnetic field. It is then rotated so that it becomes perpendicular to the field.
(i) Derive an algebraic expression for the ratio F60F90 of the forces acting on the wire in the two orientations. (Here F60 corresponds to the 60∘ position and F90 to the 90∘ position.)
(ii) Using your expression, calculate the value of the ratio when L=0.18m, I=7A, and B=0.35T.
(iii) Determine the percentage increase in the magnitude of the force when the wire is rotated from 60∘ to 90∘. Show all working steps.