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Electric Fields and Dielectrics
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How does the alignment of charges within a dielectric material under an external electric field affect the force calculated using Coulomb's Law?

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Choose the Best Answer

A

It reduces the effective force between charges due to polarization.

B

It increases the effective force between charges, making them attract more strongly.

C

It has no effect on the force calculated by Coulomb's Law.

D

It reverses the direction of the force between the charges.

Understanding the Answer

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Answer

When an external electric field is applied to a dielectric, the positive and negative charges inside the material shift slightly in opposite directions, creating tiny dipoles that line up with the field. This alignment produces a polarization field that opposes the external field, effectively weakening the net field between the external charges. As a result, the Coulomb force calculated between the charges is reduced compared to the vacuum case. For example, a 1‑meter‑long rod of glass between two charges will feel a smaller attraction than if the space were empty, because the glass’s aligned dipoles partially cancel the external field. Thus, the force predicted by Coulomb’s Law must be adjusted downward to account for the dielectric’s polarization.

Detailed Explanation

When a dielectric material is placed between two charged objects, the molecules in the material tilt to align with the electric field. Other options are incorrect because The misconception here is that adding a material always makes objects attract more; Many think the dielectric does nothing to the force, but the dielectric changes the electric field strength.

Key Concepts

Coulomb's Law
Polarization in Dielectrics
Topic

Electric Fields and Dielectrics

Difficulty

medium level question

Cognitive Level

understand

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