# The effect of an external substance on the electric force between two charges

• hokhani
In summary, placing a substance (conductor, insulator, etc.) between two opposite charges does not change the force between the two charges, but it does increase the total force on each charge due to the superposition of the original field and the extra electric field induced on the substance. The force between the two charges may be considered independent of other effects, but it can also be viewed in terms of the resultant force on each charge. Additionally, the electric field may be shielded or polarized depending on the material placed between the two charges. The concept of an effective distance between charges may also be considered when a dielectric is placed in between two charges.
hokhani
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them? It seems that the force between the two charges doesn't change but the total force on each charge increases because of the superposition of the original field of the other charge and the extra electric field due to the induced charge on the substance. I would like to know if I am wrong.

That depends on how you count the forces. What you described is one possible way to view the problem.

mfb said:
That depends on how you count the forces. What you described is one possible way to view the problem.
If we had for example a thick wood between the two point charges, ##q_1## and ##q_2##, can we say that:
the force between the two charges is ##F=kq_1q_2/r^2## and the resultant force (sum of the this force and the effects of other charges inside the wood) on each charge is zero? In other words, is the force between the two charges independent of any other effect?

hokhani said:
and the resultant force (sum of the this force and the effects of other charges inside the wood) on each charge is zero?
Why would it be zero?
hokhani said:
In other words, is the force between the two charges independent of any other effect?
That is one way to consider forces. It is not necessarily always the easiest approach.

hokhani said:
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them? It seems that the force between the two charges doesn't change but the total force on each charge increases because of the superposition of the original field of the other charge and the extra electric field due to the induced charge on the substance. I would like to know if I am wrong.
If you put a conductor between two charges, doesn't the electric field vanish inside ?

hokhani said:
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them? It seems that the force between the two charges doesn't change but the total force on each charge increases because of the superposition of the original field of the other charge and the extra electric field due to the induced charge on the substance. I would like to know if I am wrong.

Maybe you need to look at what happen to the electric field when you insert a dielectric in between the plates of a capacitor.

Zz.

mfb said:
Why would it be zero?
I think a thick wood shields the electric field and so each charge doesn't feel the effect of the other charge.

thierrykauf said:
If you put a conductor between two charges, doesn't the electric field vanish inside ?
Right, It does. But I want to know the force between the two charges and compare it with the total force (the resultant force due to the two charge and the induced charge on the conductor surface) each charge.

ZapperZ said:
Maybe you need to look at what happen to the electric field when you insert a dielectric in between the plates of a capacitor.

Zz.
The main question is:
How does the force between the two point charges change if we put a conductor between them? (increase, decrease or no change)

hokhani said:
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them?

conductor between the charges gets polarized.

#### Attachments

• 2017515-121045312-3163-6-dielectric-polarisation.jpg
41.5 KB · Views: 375
hokhani said:
The main question is:
How does the force between the two point charges change if we put a conductor between them? (increase, decrease or no change)

Maybe you should re-read your own post. Here's what you wrote in the original first post:

hokhani said:
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them? It seems that the force between the two charges doesn't change but the total force on each charge increases because of the superposition of the original field of the other charge and the extra electric field due to the induced charge on the substance. I would like to know if I am wrong.

I simplified one part of the question by suggesting something that you can look up easily as an analogous situation. but I guess learning something is not what you're interested in.

Zz.

ZapperZ said:
Maybe you should re-read your own post. Here's what you wrote in the original first post:
Although the main question was about placing a conductor between the two point charges, I raised the question generally (for conductors and insulators and ...), and exactly stated what I like to know.

ZapperZ said:
I simplified one part of the question by suggesting something that you can look up easily as an analogous situation.
My question is beyond the well-known dielectric effect which decreases the electric field between the two capacitor plates. This clear effect is explained exactly in the elementary textbooks.
ZapperZ said:
but I guess learning something is not what you're interested in.

Last edited:
hokhani said:
How does the force between the two opposite charge change if we place a substance (conductor, insulator, ...) between them?

No liability assumed. Your question is sometimes addressed in terms of an “effective distance between charges” in case a dielectric slab of a given thickness is placed in between two charges in vacuum.

Last edited:
hokhani

## 1. What is the electric force between two charges?

The electric force between two charges is the force that acts between two charged particles. It is a fundamental force of nature that is responsible for the interactions between charged particles.

## 2. How does an external substance affect the electric force between two charges?

An external substance can either increase or decrease the electric force between two charges, depending on the properties of the substance and the charges involved. For example, an insulating material can decrease the force by reducing the amount of charge that can flow between the two charges, while a conducting material can increase the force by allowing more charge to flow.

## 3. What types of external substances can affect the electric force between two charges?

Any substance that can interact with charges, such as insulators, conductors, and semiconductors, can affect the electric force between two charges. Other factors, such as temperature and pressure, can also have an impact on the force.

## 4. Can an external substance completely cancel out the electric force between two charges?

No, an external substance cannot completely cancel out the electric force between two charges. The force will always exist to some degree, but it can be weakened or strengthened by the presence of external substances.

## 5. What are the practical applications of studying the effect of external substances on the electric force between two charges?

Understanding how external substances affect the electric force between two charges is important in various fields such as electronics, materials science, and engineering. It can also help in developing new technologies and improving existing ones, such as in the design of electronic devices and the development of new materials with specific electrical properties.

• Electromagnetism
Replies
3
Views
832
• Electromagnetism
Replies
16
Views
1K
• Electromagnetism
Replies
6
Views
926
• Electromagnetism
Replies
2
Views
783
• Electromagnetism
Replies
15
Views
1K
• Electromagnetism
Replies
17
Views
2K
• Electromagnetism
Replies
73
Views
3K
• Electromagnetism
Replies
11
Views
942
• Electromagnetism
Replies
7
Views
1K
• Electromagnetism
Replies
48
Views
3K