Write an expression for B⃗ (d), the magnetic field a distance d above the xy plane of the sheet. Use μ0 for the permeability of free space. Express the magnetic field as a vector in terms of any or all of the following: d, I, N, a, μ0, and the unit vectors i^, j^, and/or k^.

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.