I have a question about current densities. My understanding is that there are 3, volumic $(\vec{J})$ , surface $(\vec{K})$ and linear $(\vec{\lambda})$. The first question is, that if J is volumetric, why is it used in the equation $I=\int_s \vec{J} d\vec{S}$. The second is, if J has units A/m^2 and K A/m, does lambda have units of A? how does it differ then with Current Intensity?