Physics - Higher Potential or Lower Potential?
The problem is that there are two plates. One (plate A on left) is with positive charges and other (plate b on right) negative charges. They are at a distance 1.5cm but I am not worried about solving for anything I need help understanding stuff instead. Here is what I understand: Electrical field is going from left to right because it goes away from positive and attracts to negative. -->(-)<-- ; <--(+)-->. What I don't understand is why plate A is at higher potential. How do you know? thanks in advance for everyone help!
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Verified answer
Try imagining placing a (positive) charge close to plate A. As you've already said, the electric field lines are going from left to right, so when there is a positive charge that's the way it will move! But to start moving, the charge needs kinetic energy and it has to get it by using up electric potential energy from the electric field. As the charge moves along , the kinetic energy increases and the potential energy decreases. When the charge gets to plate B, all the potential energy has been used up and converted to kinetic energy.
Potential is defined as the 'the potential to do work' or 'the potential for a transfer of potential energy to kinetic energy'. What this means is that the potential is higher where there is more energy available to do work.
So, there was more potential energy at plate A then plate B, so we say that the potential is higher!
In an electric field, potential is defined as the potential energy per unit charge, so it's basically a measure of how much potential energy a charge would have at every point in an electric field.
Electric Potential at a point refers to how much energy it takes to bring a unit positive charge from infinity to that point. At infinity the potential is taken to be zero. In moving a unit positive charge from infinity to a positive plate, you have to do a lot of work because they repel each other. Just like you have to do a lot of work to lift an object and give it gravitational potential energy. If you let the positive particle go at that point the electric field can do work on the object and you get back your energy in the form of kinetic energy, just like dropping a ball converts potential to kinetic energy.
For a negative plate, you do a negative amount of work to move a positive charge because they attract each other, just like when lowering a mass you do negative work. It is the field that does positive work. It would take energy to move the positive charge to infinity, so it has negative potential energy.