Determining a charge at higher potential & potential energy

[chococho]

**sorry, the title should probably read determining a point at higher potential and potential energy
So I feel like this is a really simple example, but I have a test tomorrow and this potential and potential energy stuff is really starting to not make sense...

I know that a charge going in the direction of the electric field goes from a higher potential to lower potential and from lower to higher if it's going in the opposite direction.
The problem is that I don't know how potential energy is different from potential.

So a diagram I have has two points A and B and an electric field going from right to left. There is also a positive charge just sitting between A and B. And it says PE for B is bigger than PE for A. Is this just because B is at a higher potential?

I also have a diagram that is the same, but only with a negative charge between A and B instead of a positive charge. This one I'm not really sure about.. I assumed it would be the opposite for a negative charge, but it says Vb is bigger than Va, but Ua is bigger than Ub.

Can somebody help me with this please? The more I think about it the more confusing it gets...

 

[UltrafastPED]

If the potential is V, then the potential energy is qV.

That is, it needs to be multiplied by the charge. You can remember this easily if you are familiar with electron volts: eV. One eV is the energy acquired by an electron moving through a potential difference of 1 volt.

 

[chococho]

Hm, that's something we never learned in class..
Could you also explain the difference between what happens when you have a positive charge or a negative charge in the field?

 

[jtbell]

I also have a diagram that is the same, but only with a negative charge between A and B instead of a positive charge.

Now you know that U = qV. If q is negative, what happens to U?

This one I'm not really sure about.. I assumed it would be the opposite for a negative charge, but it says Vb is bigger than Va, but Ua is bigger than Ub.

When you have a quantity that can be either positive or negative, it's less confusing to say "higher" instead of "bigger", and "lower" instead of "smaller". If V_b = (say) 5 volts, and V_a = 3 volts, then V_b is higher than V_a (V_b > V_a).

However, if If U_b = -5 joules, and U_a = -3 joules, then U_b is lower than U_a (U_b < U_a).

 

[sardar]

I can help clarify the concept of potential and potential energy for you. Potential is the measure of the electric field at a specific point in space. It is a scalar quantity, meaning it only has magnitude and no direction. Potential energy, on the other hand, is the energy that a charge possesses due to its position in an electric field. It is a vector quantity, meaning it has both magnitude and direction.

In your first diagram, the positive charge is moving from point A to point B in the direction of the electric field. This means that the charge is going from a higher potential at point A to a lower potential at point B. Since potential energy is directly proportional to potential, the potential energy at point A would be lower than at point B.

In the second diagram, the negative charge is moving in the opposite direction of the electric field, from point B to point A. This means that the charge is going from a lower potential at point B to a higher potential at point A. Since potential energy is inversely proportional to potential, the potential energy at point B would be lower than at point A.

I hope this helps clarify the difference between potential and potential energy for you. Remember, potential is a measure of the electric field, while potential energy is the energy of a charge in that electric field. Good luck on your test tomorrow!