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

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Homework Help Overview

The problem involves calculating the electric field strength across a membrane given a voltage and thickness. The context is within electrostatics, specifically dealing with uniform electric fields.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the formula E = -V/d and question the correctness of the initial calculations. There is confusion regarding the conversion of voltage from millivolts to volts and the multiplication involved. Some participants suggest using unit analysis to clarify the relationships between voltage and electric field strength.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the calculations and questioning the signs of the results. Some have provided alternative calculations and are seeking validation of their approaches.

Contextual Notes

There are indications of potential misunderstandings regarding unit conversions and the implications of the negative sign in the electric field equation. The original poster expresses uncertainty about the correctness of their results.

elowe93
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Homework Statement



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.

Homework Equations



E=-Vd

The Attempt at a Solution



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

i don't understand why this is wrong?
 
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elowe93 said:

The Attempt at a Solution



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

i don't understand why this is wrong?

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.
 
You should not have multiplied.
 
use unit analysis. What are the units of an e field? what are the units of voltage?
 
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 I am finding for this it has a negative. I feel like it should be positive though is this right?
 

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