Measurements with microelectrodes have shown that a 0.30-nm-diameter potassium ion (K+) channel carries a current of 1.8 pA. How many potassium ions pass through if the ion channel opens for 1.0 ms? What is the current density in the ion channel? I am completely lost for this one. Anyone know of any equations that I can use? Current is, its I = dQ/dt, the flow of charge through a point, through time. Like measuring the flow of water through a pipe. The area the flow is going through (the inner area of the "pipe") because they give you the diameter. area = pi*r^2, 2*r = diameter. I = dQ/dt = n*A*q*dx/dt = n*A*q*Velocity so first solve I = n*A*q*Velocity then use that with velocity = dx/dt to get dx. Then use dQ = (n*A*dx)*q to get dQ. But I am stuck on how to solve for the variables and how to complete the problem. Can anyone help me out with the answer?