# Incomprehensible part in Griffiths' text

• WiFO215
In summary, Griffiths states that the energy required to construct a point charge using the above formula would be infinity, but this is a problem with classical EM theory.
WiFO215
After deriving the self energy, or the energy to construct a charge configuration$$\frac{\int_{V} \epsilon E^{2}dV} {2}$$(where V is the volume over which the E-field of the configuration extends.)

Griffiths goes on to say that the energy required to construct a point charge using the above formula would be infinity. With this statement, I can agree. But then he also adds that this is a big problem with classical EM theory. I cannot comprehend that. I don't quite see the problem.

Remember when we were dealing with the field of an infinite sheet? The field turns out to be a constant,

$$\frac{\sigma}{2 \epsilon}$$

where $$\sigma$$ happens to be uniform charge density over the infinite sheet. In that problem, when we set the zero of the potential at infinity, the problem got very messy. Potentials would always shoot to infinity. That problem was crucial (at least to me) in showing that one ought to be careful in setting the zero of the potential.

If we carry over what we've learnt, then the "problem" of infinities of a point charge disappear. In deriving the above formula for energy of a point charge, he sets the zero at infinity. Why not just set the zero AT the point charge in this problem? Wouldn't that solve the problem?

Last edited:
anirudh215 said:
Why not just set the zero AT the point charge in this problem? Wouldn't that solve the problem?

Please take a look at what is set to zero. Is it the field or is it the potential? What difference does that make? <--- There's a hint in my wording.

Also put a finite charge q on a finite sheet of area A. As the area of the sheet increases, the charge density decreases as σ' = Aσ/A'. So the field drops off with length squared as dimensions increase to ∞.

Bob S

## 1. What is the "incomprehensible part" in Griffiths' text?

The "incomprehensible part" in Griffiths' text refers to a section or concept that is difficult for the reader to understand due to complex or unclear language, equations, or ideas.

## 2. Why is there an "incomprehensible part" in Griffiths' text?

The "incomprehensible part" is not intentional, but rather a result of the complexity of the subject matter or the author's writing style. It is common for scientific texts to have sections that are challenging for readers to grasp.

## 3. How can I better understand the "incomprehensible part" in Griffiths' text?

One way to better understand the "incomprehensible part" is to read it multiple times and break it down into smaller sections. It can also be helpful to look up unfamiliar terms or equations and seek clarification from other sources or experts in the field.

## 4. Is the "incomprehensible part" in Griffiths' text important to understanding the overall text?

Yes, the "incomprehensible part" is often a crucial component of the text and is necessary for a complete understanding of the topic. Skipping over it may result in a lack of understanding of the entire text.

## 5. Are there any resources available to help with understanding the "incomprehensible part" in Griffiths' text?

Yes, there are various resources available such as discussion forums, online tutoring, and study guides that can assist in understanding difficult concepts in Griffiths' text. Additionally, reaching out to colleagues or the author themselves may provide further clarification.

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