Hi All,

Currently I am reading a book "Matters and interactions". In chapter 18 - Page 724 author asked reader to do the exercise about the electric field in the wire. here are the exact words below:-

"At the locations marked X on a copy of Figure 18.16 (locations 1 through 5), draw arrows representing the approximate electric field due solely to the charges on the metal plates of the mechanical battery. (The amount of charge on the belt is completely negligible compared to the charge on the plates.) Forget the presence of the wire for the moment."




Next he asked for another exercise which is " Next, in a different color or with a different-looking arrow, indicate the drift velocity of the mobile-electron sea at those locations, assuming that the drift velocity is due solely to the electric field made by the charges on the plates of the mechanical battery"



"Good grief! Figure 18.17 shows that we’ve got the electron current running upstream at location 4 in the wire! That can’t be right in the steady state (the situation in which charge distributions and currents are not changing). We are forced to conclude that in the steady state there must be some other charges somewhere that contribute to the net electric field in such a way that the electric field points upstream everywhere (giving an electron drift velocity downstream everywhere)."



If we check the electric field it is from positive to negative and here if we see the location of electric field at point 4, it is towards the negative terminal of the battery, but in the very next figure in 18.17 author takes the electric field in opposite direction, I dont understand his logic at point 4 that why he takes the direction of electric field in opposite direction, technically at point 4 it should not be towards the positive plate of the battery. Can any one understand this ?? please help

 

It might make things easier to think about the polarity of the field rather than the direction. If you think of one plate as being positive (or negative) does that make it easier to think about?

 

It might make things easier to think about the polarity of the field rather than the direction. If you think of one plate as being positive (or negative) does that make it easier to think about?

Polarity decides the direction mate

 

It might make things easier to think about the polarity of the field rather than the direction. If you think of one plate as being positive (or negative) does that make it easier to think about?

I am asking about how would have he calculated the electric field direction

 

I am asking about how would have he calculated the electric field direction

IMO all the book chapter is saying is that the charges in the wire move to neutralize the applied electric field generated across the plates from mechanical charge separation (an external force) and how surface charges develop.
https://matterandinteractions.org/videos/EM.html

 

IMO all the book chapter is saying is that the charges in the wire move to neutralize the applied electric field generated across the plates from mechanical charge separation (an external force) and how surface charges develop.
https://matterandinteractions.org/videos/EM.html

Well i understand they are trying to emphasize that electric field is being developed from the surface charges but i am confused that how he had calculated the electric field there at first place ?

 

Well i understand they are trying to emphasize that electric field is being developed from the surface charges but i am confused that how he had calculated the electric field there at first place ?

What is there to be confused about? The video using the text book explains the process in detail. Review the previous book material to remove any personal confusion. The problem is not in the book.

 

What is there to be confused about? The video using the text book explains the process in detail. Review the previous book material to remove any personal confusion. The problem is not in the book.

I checked the complete video now, i understand he is just taking the reference with respect to electron movement