Quantum mechanically when you measure the position accurately, you will observe uncertainty in momentum. While one measure the momentum exactly uncertainty comes in position. The product of these two uncertainties is equal to hbar.

“Particle in a box or in an infinite potential well” this statement is a representation of a physical problem. As you know in a conductor for the current flow of free electrons are responsible. You know these free electrons doesn’t escape from the conductor surfaces. It means they are bound with in the boundary of material. The surfaces of conductor is treated as high potential walls. Particle that is electron is free to move inside the conductor.