Conceptual question on field/displacement

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In summary, the relationship between electric field and displacement can be understood by considering the polarization of a dielectric material and defining its permittivity. However, the concept of displacement as an independent variable may be confusing. To understand this, one can imagine the superposition of fields from many dipoles, where the resulting field will be parallel to the polarization. This is similar to the relationship between stress and strain in materials.
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johng23
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I have a very basic problem in understanding the relationship between electric field and displacement. If a field is applied to a dielectric, it is clear that this will cause the material to polarize, and one can define the permittivity of the material to quantify the size of this effect. Since we can write [itex]D=\epsilon E[/itex], we can also define the inverse permittivity [itex]E=\kappa D[/itex]. But conceptually, I can't make sense of the displacement as the independent variable. How does a polarization give rise to a macroscopic field in the same direction? If anything, a polarization seems associated with a field in the opposite direction (by imagining the situation in the center of a dipole), although I know that macroscopic E&M says nothing about these microscopic fields.

If I think about the case of stress and strain, I can easily imagine how either one gives rise to the other. Where is my problem?
 
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Ok, the answer is just to take the superposition of the fields from many dipoles. Everything should cancel except the field parallel to the polarization.
 

1. What is the difference between field and displacement?

Field refers to a physical quantity that varies in space and time and can exert a force on a test particle, whereas displacement is the change in position of an object from its initial to final position.

2. How do we measure field and displacement?

Field can be measured using instruments such as voltmeters, magnetometers, or accelerometers. Displacement can be measured using rulers, measuring tapes, or more advanced tools such as GPS devices.

3. What factors affect the magnitude of field and displacement?

The magnitude of field can be affected by the distance from the source of the field, the strength of the source, and the type of field. Displacement can be affected by the initial and final positions of the object, as well as any external forces acting on the object.

4. How are field and displacement related to each other?

Field can cause displacement, as a force exerted by a field can cause an object to move. On the other hand, displacement can also affect the field, as the presence of an object can alter the strength or direction of a field.

5. What are some real-world examples of field and displacement?

A common example of field is the Earth's gravitational field, which can exert a force on objects and cause them to fall towards the ground. An example of displacement is a car moving from one location to another, where the displacement is the change in position of the car.

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