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I am am bit confused in the concept of electric potential. Does this means there is a decrease in the potential energy. Suppose a point has( - 40V) potential, does this means that the place from where the potential was measured is 40 v higher in potential.. Too confusing.!!! Plz help

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  • $\begingroup$ Voltage is a potential difference. It doesn't matter what the potential at any one point is. The only thing that matters is that there is a potential difference of 40V between two points, which, if we move a Coulomb of charge, will give (or take) us 40J of work. $\endgroup$ – CuriousOne Jun 16 '16 at 8:11
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You can always see potential as an 'energy difference' between two points.

For example in some physical problem you choose a certain zero point of energy and you take that as a reference point for the other energies in the problem. You can define that the potential energy of a mass is zero when it is at a certain height and then calculate the potential energies of different heights relative to the reference point.

Potential energy in electrostatics works similar. It is very common to define the reference point at infinity. You then say that a charge at infinity does not have any potential energy. (This makes sense because the electric and magnetic field decay when you move away from the source).

When a charge has a potential energy of -40V that means that it has a lower potential energy than it had at the reference point. For example: I have a charge configuration somewhere with mostly positive charges. Now I take a negative charge and bring it from infinity to the charge configuration. Because the charges attract eachother the potential energy of the negative charge has decreased. It could for example be -40V times the negative charge. (The negative charge has however picked up kinetic energy).

So what it really means when a potential is negative is that the potential energy is lower than it would be if the system was in the reference situation.

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