as the marked region is nearer to surface with positive charge density should there be a net electric field instead of 0?
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$\begingroup$ Compared which charge density are you saying that the positive charge density is lesser? $\endgroup$– gontu sandeepCommented Jan 13, 2022 at 4:50
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$\begingroup$ The density of the positive charges is greater than the negative charges, and this compensates for the closer distance as compared to the negative charges to give a zero net field. $\endgroup$– Ambica GovindCommented Jan 13, 2022 at 6:04
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$\begingroup$ Please post your comments about the answer below the answer itself. $\endgroup$– Ambica GovindCommented Jan 13, 2022 at 6:05
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$\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$– Community BotCommented Jan 13, 2022 at 7:37
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2 Answers
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The net electric field inside a conductor is zero because it is not just the field generated by the surface charges, it is the sum of that with the external electric field.
Remember that in order to polarize a material like this you need to put it in an external electric field. This electric field causes the charges of opposite sign to accumulate on opposite surfaces. They do so in such a way that the field they generate exactly cancels the external field.
This external field can be generated by, for example, a charged sphere or capacitive plates surrounding the conductor without touching it.
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$\begingroup$ Thank you that clarifies it. But it's hard to believe that there always exists a possible distribution of charges along the surface of a conductor as to cancel electric field everywhere inside itself. $\endgroup$ Commented Jan 13, 2022 at 15:25
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An important property of conductors is that every point inside it has no net electric field. This is achieved by conductors by rearranging the charges on the surface in such a way that every point inside the conductor has no net field. If the conductor is not a perfect sphere in shape, the charge could be distributed non-uniformly to achieve this.
You could think of it this way: If the net electric field were not zero, the charges inside the conductor would always experience a force and there would be current flow! And when we are talking about electrostatic conditions, there cannot be current flow, and hence no net electric field inside the conductor can exist.
In the diagram, the positive charges are definitely closer to your point, but the density of positive charges is also lesser, and thus the reduced charge density on the surface compensates for the field of the negative charges plus the external electric field, resulting in a zero net field.
answered Jan 13, 2022 at 4:44
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$\begingroup$ About the shape affecting charge distribution. Yes indeed! The effect of an object with a sharp point is very interesting reading tht the question poster should search up. $\endgroup$– DanCommented Jan 13, 2022 at 4:59
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$\begingroup$ But why there is more negative charge? $\endgroup$ Commented Jan 13, 2022 at 6:26
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$\begingroup$ There isn't more negative charge; the overall conductor remains neutral. There's more negative charge density. $\endgroup$ Commented Jan 13, 2022 at 7:21
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$\begingroup$ If there is more negative charge density, then a similar point inside the conductor but near the negative charges would have a non zero field according to this line of thought: the point is closer to negative charges and there is more negative charge density, so there is no way that the positive charges contribution cancel the negative one $\endgroup$ Commented Jan 13, 2022 at 10:06
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1$\begingroup$ @LucasBaldo Thanks for pointing that out, forgetting to mention the external field rendered the answer entirely incorrect. I have made the necessary edits. $\endgroup$ Commented Jan 13, 2022 at 11:59