# Potential lowering effect on a positively-charged plate

Suppose the following situation:

A positively-charged plate, not connected to any e.m.f. source, is brought near a neutral block of conductor material. Naturally, negative charges are induced on the side of the conductor material that is closer to the plate.

I would like to ask what is the change to the potential of this positively-charged plate due to the induced negative charges on the conductor material.

My physics teacher has been trying to convince me that the plate's positive potential decreases as he tells me that the electric field created by the induced negative charges causes the potential of everything in its vicinity to be lowered.

However, I intuitively thought that the potential of the positively-charged plate should increase since the induced negative charges would repel negatively-charged particles in the plate and cause the side of the plate closer to the induced negative charges to become more positively-charged, increasing its positive potential.

• This is basically method of image charges May 20, 2020 at 12:20

The potential difference between two points equals the work required per unit charge to move the charge between the points. For a uniform electric field $$E$$ the work required to move a charge $$Q$$ a distance $$d$$ is $$QEd$$. Therefore the potential difference between the points is $$Ed$$.

The polarization of the previously neutral conductive block creates an electric field in the block opposing the field of the positively charged plate, though there is no net field within the block. This reduces the effective electric field of the positively charged plate. The phenomena is similar to the effect of the polarization of a dielectric between capacitor plates that reduces the effective field between the plates. For a discussion of this refer to the following link:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dielec.html

Since the effective field $$E$$ of the positively charged plate is reduced, the potential difference between two points in the field is reduced.