# Electric field lines

PhysicStud01
Homework Statement:
The top plate is negatively charged and the bottom earthed.

which of the diagrams is correct?
Relevant Equations:
none
Shouldn't the plate that is earthed be with no charge? making B correct.

but the accepted answer was A.

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Shouldn't the plate that is earthed be with no charge?
No, grounded means zero potential, not zero charge.

PhysicStud01
No, grounded means zero potential, not zero charge.
so, even if it's zero potential, it's possible to have +ve charges?
shouldn't the plate with +ve charges be at a higher potential

Staff Emeritus
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so, even if it's zero potential, it's possible to have +ve charges?
Yes, that is perfectly possible. You can also have negative charges. It depends on what charges exist in the surroundings. What characterises ground is zero potential.

shouldn't the plate with +ve charges be at a higher potential
Higher relative to what? Let me give you a different example where there is no ground:
Consider two spherical concentric shells with the same magnitude charge. The outer shell is positively charged and the inner is negatively charged. Since the overall charge of the system is zero, there is no electric field outside of the outer charge and therefore its potential is zero (assuming potential at infinity is set to zero) although it is positively charged.

Yes, the grounded plate will have a higher potential than the negatively charged one, but this tells you nothing about the actual charges on the plate.

Suboor hashmi
The plate which is grounded should have zero charge on its left face so charge on outer face of 2 plate also have zero charge, so negative charge of 2 plate will appear on inner face and equal and opposite charge induce on inner surface of grounded plate then electric field will move from positively charged face to negatively charged face

PhysicStud01
then can we say that the field lines are from high potential to low potential instead of from +ve to -ve?

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