# Help finding the electric feild strength in a uniform E-field

1. Jul 2, 2014

### elowe93

1. The problem statement, all variables and given/known data

The voltage across a membrane forming a cell wall is 78.7 mV and the membrane is 8.52 nm thick. What is the electric field strength? (The value is surprisingly large, but correct.) You may assume a uniform E-field.

2. Relevant equations

E=-Vd

3. The attempt at a solution

E=-(.00787V(8.52e-9m)) = 7.9e-11 V

i dont understand why this is wrong?

Last edited by a moderator: Jul 2, 2014
2. Jul 2, 2014

### jk86

The problem stated that the voltage was 78.7 mV, but you have written that down as 0.00787=7.87mV. Also check your multiplication.

3. Jul 2, 2014

### rude man

You should not have multiplied.

4. Jul 2, 2014

### BiGyElLoWhAt

use unit analysis. What are the units of an e field? what are the units of voltage?

5. Jul 2, 2014

### elowe93

Okay, so i did E=(.0787)/(8.52e-9) to get 9237089 V/m is this correct? or should it be negative because in some of the equations im finding for this it has a negative. I feel like it should be positive though is this right?