# Homework Help: Electric Field in a living cell

1. Jan 23, 2008

### arod2812

1. The problem statement, all variables and given/known data
The membrane surrounding a living cell consists of an inner and an outer wall that are separated by a small space. Assume that the membrane acts like a parallel plate capacitor in which the effective charge density on the inner and outer walls has a magnitude of 5.77 x 10-6 C/m2. (a) What is the magnitude of the electric field within the cell membrane? (b) Find the magnitude of the electric force that would be exerted on a potassium ion (K+; charge = +e) placed inside the membrane.

2. Relevant equations
I don't understand what the second part of this question entails. What does +e tell me?

3. The attempt at a solution
I think i understand that the first part is E=5.77E-6/8.8542E-12 because E=sigma/E(not)
Therefore, I replace the charge density (sigma) with the charge density for an electron??

2. Jan 23, 2008

### blochwave

The positively charged potassium ion is missing an electron, so its charge +1.602x10^-19 coulombs, that's what +e means

I believe you did part a) right, as long as your equations and numbers are right

Regardless, it's similar to the other problem you posted. You have found the electric field in part A, and now you wanna know the force exerted on a charge +e by that electric field. Same equation you used in the other problem