Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Question 5

  1. Feb 4, 2005 #1
    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?
  2. jcsd
  3. Feb 4, 2005 #2
    Some helpful steps :
    Remember what current is, its I = dQ/dt, the flow of charge through a point, through time. Like measuring the flow of water through a pipe.
    Simple calculus, or just realizing what it means can give you the equaiton
    You know 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.
    The CHARGE thats flowing through with each ion is what? Do you understand what it is? Its a K+ ion, so you need to understand what charge it is carrying (in terms of electron charge). Its quite simple.
    I think you had a similar equation to what you need now.
    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.
    Thats a start. I think its right, I can be wrong.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook