1. The problem statement, all variables and given/known data It is said that the potential in the neutral regions of a PN junction diode is CONSTANT. 2. Relevant equations V=Q/4ΠΣr 3. The attempt at a solution It is said in all textbooks to ASSUME that the electric field in the neutral regions as zero. Two aspects confuse me. 1. What charges cause the CONSTANT potential in the neutral region? Is it the charges in the depletion region or the charges in the neutral region(even though net charge is zero there are still charges in the neutral region,which can a cause a potential,right?) As, for a point in space to have a potential there must be a charge involved since V=Q/4ΠΣr 2. If the potential is due to the charges in the depletion region, how can it be constant through out the neutral region? Since as we move away from the depletion region charges through the neutral region doesn't 'r' in the equation,V=Q/4ΠΣr vary? Please don't give an answer like since electric field is zero the potential is constant, since i don't think that is a fundamental way to think about it. Please give an answer in terms of the fundamental DEFINITION of Electric Potential. Thanks in advance.