# Electrodynamics problem: charge origin?

• Wiemster
In summary, the conversation discusses an electrodynamics problem involving a conductor with an insulating region and an electric field applied. The problem involves understanding the origin of charges on the surface of the insulator and their role in diverting currents. It is determined that the charges responsible for this are not bound charges of the insulator, but rather a pileup of free charges in the conductor. The conversation also touches on the concept of surface charges canceling out the normal component of the electric field.
Wiemster
[SOLVED] Electrodynamics problem: charge origin?

When you have an insulating region within a conductor and an electric field is applied such that a current flows, this current will be made to move around the insulating region.

-I assume a charge distribution will arise on the surface of the insulator to make this possible

with an electric field to the right, to divert the currents flowing to the right one needs a positive charge at the left of the insulator to divert these currents around it; the situation is then:

E---> + I - (with + &- the surface charges and I the insulator)

But this is opposite of what one would expect from bound charges in an electric field. Here one would expect the postive charge to displace along the direction of the electric field so that -I+ will occur. What is happening here phsyically? Are the charges not the bound charges of the insulator but actually a pileup of free charges making up the currents in the conductor? Why then don't they just go around the insulator? Or is my view that charges are responsible for diverting the currents around the insulator incorrect?

-I also assume that in order to have no currents flowing into the insulator the component of the current normal to the sphere vanishes just outside it, which will mean the normal component of the electric field has to vanish there as well.

I'm figuring this will have to be the case and surface charges being responsible for the cancellation of the (normal component of the) electric field. But what then is the origin of these charges as they do not seem to be bound charges of the insulator?

I'm sorry, I saw problems where there were none. I get it now.

The origin of these charges on the surface of the insulator is due to the movement of free charges within the conductor. When an electric field is applied, it exerts a force on the free charges, causing them to move and create a current. As the current flows around the insulating region, it creates a build-up of charges on the surface of the insulator. These charges are not bound charges of the insulator, but rather a result of the movement of free charges within the conductor.

The reason why these charges do not just go around the insulator is due to the insulator's properties. Insulators have a high resistance to the flow of current, so the charges are unable to pass through it. Instead, they accumulate on the surface of the insulator, creating the necessary electric field to divert the current around it.

In order for there to be no current flowing into the insulator, the normal component of the electric field must be zero just outside of it. This is because the insulator acts as a barrier to the flow of current, and any electric field normal to its surface would cause the charges to move into the insulator. The surface charges on the insulator are responsible for canceling out this normal component of the electric field, ensuring that the current is diverted around the insulator.

Overall, the origin of the charges on the surface of the insulator is due to the movement of free charges within the conductor and the properties of the insulator itself. These charges play a crucial role in creating the necessary electric field to divert the current and prevent it from flowing into the insulator.

## 1. Where do charges come from?

Charges are fundamental particles that exist in nature. They can be found in atoms, which are composed of positively charged protons, negatively charged electrons, and neutral neutrons. Charges can also be created through various physical processes such as friction, contact, and induction.

## 2. How are charges distributed in an object?

The distribution of charges in an object depends on the material's properties and the external factors acting on it. In conductors, charges are free to move and distribute evenly on the surface due to the repulsion between them. In insulators, charges are not free to move, and they usually remain localized in specific areas.

## 3. What is the role of electric fields in charge origin?

Electric fields are responsible for the movement and interaction of charges. They occur due to the presence of charged particles and can be created by electrically charged objects or through changes in magnetic fields. Electric fields are essential in the origin and behavior of charges.

## 4. Can charges be created or destroyed?

According to the law of conservation of charge, charges cannot be created or destroyed. They can only be transferred from one object to another or converted into different forms, such as electrical energy. This means that the total amount of charge in a closed system remains constant.

## 5. How does the movement of charges affect electromagnetic phenomena?

The movement of charges is the basis of all electromagnetic phenomena. When charges are in motion, they create a magnetic field, and when they are accelerated, they produce electromagnetic waves. Electromagnetic phenomena, such as electricity, magnetism, and light, are all related to the movement and interaction of charges.

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