Electrical Potential Energy

[seraphkz]

I understand that the Electrical Potential Energy increases when LIKE charges are brought towards each other. Why does the Electrical Potential Energy decrease as OPPOSITE charges are brought towards each other? Don't they experience a greater force as they're brought closer together? Regardless of their charges...I thought since the electric force increases as the distance between the two charges decreases, so does the Electric Potential Energy...

And I'm getting REALLY confused with Electrical Potential Energy, Electric Field, and Voltage.

---

Members don't see this ad.

 

[Rabolisk]

All objects want to decrease their potential energy, or "use" their potential energy. Opposite charges move towards each other, decreasing their potential energy. Do you want a more rigorous, mathematical way of viewing it?

 

[seraphkz]

I think I sort of get it. Kaplan explains Electric Potential Energy as the work required to move a charge. So since opposite charges attract each other, the work required to bring them together is less when they are brought towards each other.

I just hate this chapter of physics. Voltage just confuses me, I still don't get the relationship between Voltage and Electric Potential Energy.

 

[Rabolisk]

With opposite charges, external work is required to bring them apart rather than together. Defining infinity as 0, you can see this leads to negative work for opposite charges, and positive work for like charges.

Voltage is just Electric Potential Energy per charge. You can't have a force or a potential energy with just one charge because two charges are required either to attract or repel. Potential energy, both electric and gravitational, are really energy associated with a system rather than a single object. Regardless, we say that one object creates a gravitational field and an electric field around them (if charged). Electric potential at a point is just what the potential energy of a hypothetical test charge would be at that point. One volt is defined as one joule over one coulomb.

Force = Field x Charge
Energy = Voltage (potential) x Charge

 

[seraphkz]

I see Rabolisk. Thanks so much for writing that out.

I have another question.

Let's imagine 2 plates.

++++++++++++++++++++++++++++++++++++++
*


*
-------------------------------------------------

And there are 2 POSITIVELY charged particles. Which one would experience a higher acceleration? Which one would experience a higher force?

To my understanding:
1) They would experience the SAME force: F=qE
2) Bottom one would experience a higher velocity, but same acceleration. Right?

 

[Rabolisk]

Why would one experience a higher velocity?

 

[seraphkz]

Oh oops. I meant. Let's say it's one particle, but at 2 different times. So as the particle travels to the bottom, it gains speed. Haha that's what i meant, sorry for being confusing.

 

[ilovemcat]

With opposite charges, external work is required to bring them apart rather than together. Defining infinity as 0, you can see this leads to negative work for opposite charges, and positive work for like charges.

Voltage is just Electric Potential Energy per charge. You can't have a force or a potential energy with just one charge because two charges are required either to attract or repel. Potential energy, both electric and gravitational, are really energy associated with a system rather than a single object. Regardless, we say that one object creates a gravitational field and an electric field around them (if charged). Electric potential at a point is just what the potential energy of a hypothetical test charge would be at that point. One volt is defined as one joule over one coulomb.

Force = Field x Charge
Voltage (potential) = Energy x Charge

I'd imagine this guy getting a 40+ on his mcat. He seems very knowledgeable.

 

[Rabolisk]

Hah, thanks, but I doubt that I'll get above a 35... 40 goes beyond dedication and knowledge. It requires very high intelligence.