- #1

GBC

- 3

- 0

**Sodium ion flows a through a cylindrical ion channel --> diameter = 0.85 um and is 5 um long.**

potential difference b/w the ends of the channel is 225 mV

drift velocity = 0.015 m/s

in a period of 1 ms, a total of 15*10^6 ions exit the channel

potential difference b/w the ends of the channel is 225 mV

drift velocity = 0.015 m/s

in a period of 1 ms, a total of 15*10^6 ions exit the channel

a. total charge exiting the channel in 1 ms =?

b. current in the ion channel=?

i have been trying to find b.) but I think my values might be wrong... PLEASE HELP ME!

## Homework Equations

Q=qnV

I=qnAv=Q/change in time

change in time = length/drift velocity

n=N/Vso for a. using the formula for Q:

q=1.6*10^-19

N=15*10^6

V=l*PIr^2= (5 um)(PI)(4.25*10^-7)^2=2.8*10^-18

plugging in this value to the equation of Q, I get:

Q=2.4*10^-12 (acc to the solutions on the book, this is right)

Now, my problem is b...

in this part, I used I=Q/t

i know t = length/velocity so i plug in giving me =(5 um)(0.015 m/s)

so now that i have t, i just use the Q from a to solve for I and I get 7.2*10^-9.

however, according to the solutions this is wrong. it is suppose to be 2.4*10^-9...

I have a feeling my Q value for this question is wrong since it's asking for the current IN the ion channel and the Q-value i have is the total charge exiting the channel... so how do I find the Q IN the ion channel??

please help me..!