Wednesday, October 2, 2019

Electric field due to two opposite charges


We know that The net electric field due to two equal and oppsite charges is 0.


But let us consider a charge +Q in an isolated system. An electric field E will be emitted by it.



Similarly, a -Q charge will absorb an electric field E.


When both are in the same system then the magnitude field emitted by +Q and -Q should be added.


So can it be said that an electric field 2E is between +Q and -Q.


If an electric field E is generated by +Q towards -Q


And an electric field E is generated by -Q towards itself.


If both are in same direction, shouldn't both be aded to give 2E between them.


Of course the net will remain 0.



Answer




The net electric field due to two equal and oppsite charges is 0.




This is only true if the two charges are located in the exact same location. For example, a block of copper sitting on your lab bench contains an equal amount of electrons and protons, occupying the same volume of space, so the block of copper produces no net external electric field.


But if you separate the two charges from each other, they will produce a non-zero electric field everywhere in space. (This field will get very weak, but still non-zero, at locations much further from the charges than the distance between the charges)


It's actually easier to produce "zero net field" using two equal and same-signed charges.


For example, if I have two point charges with charge $+Q$ at locations $+x$ and $-x$ on the x-axis, then they will produce zero net field at the origin, since the field from one charge will be pointing right and the field from the other will be pointing left.



So can it be said that an electric field 2E is between +Q and -Q.


If an electric field E is generated by +Q towards -Q


And an electric field E is generated by -Q towards itself.


If both are in same direction, shouldn't both be aded to give 2E between them.




Exactly.



Of course the net will remain 0.



I'm not quite sure what you mean by this.


It is true in the sense of Gauss's Law. If you construct a closed surface around the two charges then the net electric flux through the surface will be 0.


But that's not the same as saying the "net field" is 0.


The net field is measured at a point in space, and is non-zero everywhere in your system. The net flux is measured over a surface, and can be zero if you construct the surface to contain the two charges.


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