MadSci Network: Physics

Re: Why does the Electrical Field Strength differ between sheets and surfaces

Date: Mon Feb 21 06:53:39 2005
Posted By: Lawrence Skarin, Rochester Museum and Science Center Technical Assistance Group
Area of science: Physics
ID: 1108686781.Ph

Hello Thomas,

Attention to detail is important in science, and yours is good.  The 
problem here is nomenclature -- the words we use to describe things.

Sears and Zemansky, in University Physics (mine is the Third Edition from 
1964 -- Addison-Wesley) describe your Gauss's Law analyses exactly in a 
section called "Applications of Gauss's Law."

What you call a "Sheet of Charge, where the E field comes out of both 
sides of the sheet,"  Sears and Zemansky call " infinite charged 
conducting plate."

What you call a "Wall Surface where the E field comes out of only the 
surface that has the charge aligned all across it," S&Z call " 
infinite plane sheet of charge."

So your "Wall Surface" is a "sheet" in Z&K, and they analyze the infinite 
charged conducting plate as two sheets.

Each sheet contributes its own field, and the two fields can be 
superimposed.  This is called "superposition" and is often used where 
linear relations among variables exist.

So, change your "sheet" to "plate," and your "Wall Surface..." to "sheet," 
and Sears and Zemansky can help.

Thanks for your clear problem descripton -- it made finding the difficulty 

Larry Skarin

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