Electric field & Parallel plate Capacitor

In summary, the conversation discusses the change in charge density on the walls of a cell membrane when a nerve impulse propagates. The change in electric field is approximated using the formula for capacitance of a parallel plate capacitor. The typical dimensions and thickness of the membrane are mentioned and the formula for capacitance is given. The conversation also mentions the need to approximate the permittivity of the cell membrane and how to calculate the charge densities using the capacitance and electric field change.
  • #1
sci0x
83
5
Question When a nerve impulse propagates along a nerve cell, the electric field within the cell membrane changes from 7.0 x 10^5 N/C (pointing in one direction) to 3.0 x 10^5 N/C (pointing in the other direction). By approximating the cell membrane as a parallel-plate capicator, find the magnitude of the change in charge density on the walls of the membrane
 
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  • #2
Has anyone ANY ideas?
 
  • #3
What are the typical dimensions of such a cell? What is the typical thickness of the membrane? Do you know the formula for the capacitance of a parallel plate capacitor in terms of C, epsilon, Area and separation Distance? (ignoring fringe capacitance effects)
 
  • #4
Oh sorry, the thickness is 0.12 micrometres
and the parallel plate capacitor has a surface charge density of 5.9×10^-6 C/m2
 
  • #5
berkeman said:
Do you know the formula for the capacitance of a parallel plate capacitor in terms of C, epsilon, Area and separation Distance? (ignoring fringe capacitance effects)
You still need to address this part...
 
  • #6
No I don't. What is it?
 
  • #7
sci0x said:
No I don't. What is it?
C = epsilon * A / d

epsilon = permittivity
A = area of one parallel plate
d = separation of the parallel plates.

So you can take the typical dimensions for the cell membrane configuration, and calculate the capacitance (you'll need to approximate the epsilon of the cell membrane -- I have no idea what it is), and that will give you the equivalent capacitance. Given the change in electric field, you can calculate what charge change it takes to make that happen. That and the area will give you the charge densities...
 

1. What is an electric field?

An electric field is a physical field that is created by an electric charge or a changing magnetic field. It is a vector field, meaning it has both magnitude and direction, and is measured in units of volts per meter (V/m).

2. How is an electric field created?

An electric field is created by a difference in potential between two points, or by the presence of electric charges. Electric fields can also be created by a changing magnetic field, according to Faraday's law of induction.

3. What is a parallel plate capacitor?

A parallel plate capacitor is a device used to store electrical energy by creating an electric field between two conducting plates. It consists of two parallel plates separated by a dielectric material, such as air or a non-conducting material.

4. How is the electric field strength related to the distance between the plates in a parallel plate capacitor?

The electric field strength between the plates of a parallel plate capacitor is directly proportional to the distance between the plates. As the distance between the plates increases, the electric field strength decreases, and vice versa.

5. What is the formula for calculating the capacitance of a parallel plate capacitor?

The capacitance of a parallel plate capacitor is calculated using the formula C = εA/d, where C is capacitance, ε is the permittivity of the dielectric material, A is the area of the plates, and d is the distance between the plates.

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