What Happens to a Partially Inserted Dielectric in a Capacitor?

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SUMMARY

The discussion focuses on the behavior of a partially inserted dielectric in a capacitor, specifically under two conditions: constant charge on the plates and constant voltage. In both scenarios, the dielectric moves inward due to the forces acting on it. The relevant equations include the energy stored in the capacitor, \(W=\frac{1}{2}CV^2\), and the force on the dielectric, \(F=\frac{dW}{dx}\). The capacitance, \(C=εε_r \frac{A}{d}\), must be expressed in terms of the dielectric's position to analyze the system accurately.

PREREQUISITES
  • Understanding of capacitor fundamentals, including capacitance and dielectric materials.
  • Familiarity with energy equations related to capacitors, specifically \(W=\frac{1}{2}CV^2\).
  • Knowledge of force calculations in physics, particularly \(F=\frac{dW}{dx}\).
  • Basic grasp of geometry's impact on capacitance, including the role of dielectric position.
NEXT STEPS
  • Explore how to derive capacitance for a capacitor with a partially inserted dielectric.
  • Study the implications of constant charge versus constant voltage on capacitor behavior.
  • Learn about the role of dielectric constant \(ε_r\) in capacitance calculations.
  • Investigate the relationship between energy stored in capacitors and the position of dielectrics.
USEFUL FOR

Students and professionals in physics and electrical engineering, particularly those studying capacitors and dielectric materials in circuit design and analysis.

Patrikp
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  • 1. The problem statement,
Dielectric plate is placed in capacitor to the half(picture) and it can freely move. Capacitor consists of two parallel plates and is isolated. Consider two cases:
a)charges on plates are constant,
b)voltage is constant.
What happens in each case?

2. Homework Equations

$$W=\frac{1}{2}CV^2=\frac{q^2}{2C}$$
$$F=\frac{dW}{dx}\\ \text{(1)}$$
$$C=εεr \frac{A}{d} $$

The Attempt at a Solution


I know that the answer is that the dielectric will be moving inward in both cases and I even have written solution but I don't understand it. I guess that I should find force on dielectric from (2) but before that i need to determine C which I don't know how to do since dielectric is in weird position.[/B]
 

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How does the capacitance depend on the geometry of the capacitor and the dielectric partially between the plates? Write it in terms of x.

capdiel.JPG
 

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