1. The problem statement, all variables and given/known data Explain why the contribution of B°dl of the magnetic field at sections b and d of the enclosure length must be zero, even inside the solenoid. 2. Relevant equations Ampere's Law: ∮ B dl= U_0 I_enclosed N 3. The attempt at a solution The right and left sides of the loop have a magnetic field that is perpendicular to the solenoid loop. Because of this, it makes no contribution to the circulation B°dl there.