# Ion Flow Through a Channel: Current and Charge

• GBC
In summary, the conversation discusses the flow of sodium ions through a cylindrical ion channel with specific dimensions and potential difference. It also mentions the drift velocity and the total number of ions that exited the channel within a 1 millisecond period. The question at hand is to find the total charge and current in the ion channel. Using the formula Q=qnV, the total charge exiting the channel is found to be 2.4*10^-12. However, for the current in the ion channel, the correct formula to use is I=JAv, where J represents current density and A is the cross-sectional area of the channel. By using the time interval of 1 ms and the given drift velocity and dimensions, the current in the
GBC
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

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??

You were given the time interval over which the stated number of ions exited the channel. It was 1 ms. That's the timeframe that is important for figuring the current.

The drift velocity and channel dimensions are related to the current density. The time for a given ion to traverse the channel is not so important when there are many, many ions in a cross-section of the channel.

GBC and CWatters
Oh Thank you so much! I have never taken physics back in high school so this is all new to me. I was sort of confused on what it meant by "period of 1 ms" (I thought it was a typo for m/s... I have never seen millisecond used before haha) so thank you for explaining it! :)

1.

## What is ion flow through a channel?

Ion flow through a channel refers to the movement of charged particles, or ions, through a narrow pathway, or channel, within a biological or synthetic membrane. This movement is driven by a difference in electrical charge between the inside and outside of the channel.

2.

## How is current related to ion flow through a channel?

Current is a measure of the rate of flow of charged particles. In the context of ion flow through a channel, current refers to the movement of ions through the channel. The greater the number of ions flowing through the channel, the higher the current.

3.

## What factors affect ion flow through a channel?

There are several factors that can affect ion flow through a channel, including the size and shape of the channel, the concentration of ions inside and outside the channel, and the electrical charge on the channel walls. Temperature and pressure can also impact ion flow.

4.

## Why is ion flow through a channel important?

Ion flow through a channel is essential for many biological processes, such as nerve signaling and muscle contraction. It also plays a critical role in maintaining the balance of ions inside and outside of cells, which is important for overall cellular function.

5.

## How is charge related to ion flow through a channel?

Charge refers to the electrical property of particles. In the context of ion flow through a channel, charge is important because it determines how ions are attracted to or repelled from the channel walls. This attraction or repulsion affects the movement of ions through the channel and ultimately determines the direction and rate of ion flow.

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