Field between two parallel postive plate different voltages

[maxelcat]

Homework Statement

This was a one mark question on an AS paper.

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Homework Equations

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The Attempt at a Solution

Mark scheme says straight lines, equally spaced lines pointing down and starting/ending on the plates. (which I totally get if one plate was 0V or negative) However, if you place the text positive charge very close to S (+1V) won't the repulsive force from S be larger than from R meaning the overall field at that point will be upwards?

 

[andrewkirk]

Potential is a relative measure, not an absolute one. We can add or subtract the same amount to either of the potentials given and it will make no physical difference. The only thing that has a physical effect is potential difference. The lower (upper) plate will have excess negative (positive) charges on its surface because of the potential difference between the two plates, and those charges will repel any free electrons that are between the plates, whether they are near the lower or the upper plate.

 

[kuruman]

Think of the gravitational analog, when you're climbing a hill what matters is the slope (change of gravitational potential over a horizontal displacement) not how far you are above the base of the hill.