Griffiths E&M and Convention of the Sign of Potential

In summary, potential is defined as zero at infinity in Griffith's E&M, but this convention does not account for objects closer than infinity. In Mechanics, the inverse square law problems are always attractive, but in the case of a positive test charge and positive charge in question, the forces are repulsive and actually increase potential as you move closer. This may have caused confusion for Chris.
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kq6up
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I am reviewing in Griffith's E&M, and I find that potential is defined as zero at infinity (that bits fine). However, should not an object that distance from a charge be less than zero (negative) if it is closer than infinity? It seems it should as it has lost P.E. However, he doesn't seem to use this convention.

Another thought: I have just finished Mechanics in where these inverse square law problems are always attractive. I guess if my test charge was positive and the charge in question was also positive, my forces would be repulsive, and actually increasing potential as I move closer -- maybe that is why I am confused.

Thanks,
Chris
 
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kq6up said:
I guess if my test charge was positive and the charge in question was also positive, my forces would be repulsive, and actually increasing potential as I move closer -- maybe that is why I am confused.
Sounds like you figured it out for yourself! ;)

The potential about a positive charge is zero at infinity and increases as you get closer. Imagine that positive test charge being repulsed.
 
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Yes, as I was writing the question it dawned on me :D

Chris
 

1. What is the Griffiths E&M theory?

The Griffiths E&M theory, also known as Griffiths electrodynamics, is a mathematical framework that describes the behavior of electric and magnetic fields. It is based on Maxwell's equations and provides a way to calculate electric and magnetic fields in various situations.

2. What is the Convention of the Sign of Potential?

The Convention of the Sign of Potential is a rule used in the Griffiths E&M theory to determine the sign of the electric potential for a given charge distribution. It states that the electric potential is positive when a positive test charge is moved from infinity to a point in the field, and negative when a negative test charge is moved from infinity to the same point.

3. How is the Convention of the Sign of Potential related to the direction of electric field lines?

The Convention of the Sign of Potential is related to the direction of electric field lines in that it follows the direction of the electric field. When the electric field points toward a positive charge, the potential is positive. Conversely, when the electric field points away from a positive charge, the potential is negative.

4. What is the significance of the Convention of the Sign of Potential in electromagnetism?

The Convention of the Sign of Potential is significant in electromagnetism because it helps to determine the direction of the electric field and understand the behavior of electric charges. It also allows for a consistent and standardized way to calculate electric potential and electric field values in various situations.

5. Are there any exceptions to the Convention of the Sign of Potential?

Yes, there are a few exceptions to the Convention of the Sign of Potential. One exception is in the case of a dipole, where the potential is negative on one side and positive on the other. Another exception is in the presence of a point charge, where the potential is always positive regardless of the direction of the electric field. However, these exceptions do not change the overall validity and usefulness of the Convention of the Sign of Potential in electromagnetism.

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