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Suppose the plates of a parallel-plate capacitor move
Chapter 2, Problem 44P(choose chapter or problem)
Problem 44P
Suppose the plates of a parallel-plate capacitor move closer together by an infinitesimal distance ?, as a result of their mutual attraction.
(a) Use Eq. 2.52 to express the work done by electrostatic forces, in terms of the field E, and the area of the plates, A.
(b) Use Eq. 2.46 to express the energy lost by the field in this process. (This problem is supposed to be easy, but it contains the embryo of an alternative derivation of Eq. 2.52, using conservation of energy.)
Reference equation 2.52
Reference equation 2.46
Reference equation
Questions & Answers
QUESTION:
Problem 44P
Suppose the plates of a parallel-plate capacitor move closer together by an infinitesimal distance ?, as a result of their mutual attraction.
(a) Use Eq. 2.52 to express the work done by electrostatic forces, in terms of the field E, and the area of the plates, A.
(b) Use Eq. 2.46 to express the energy lost by the field in this process. (This problem is supposed to be easy, but it contains the embryo of an alternative derivation of Eq. 2.52, using conservation of energy.)
Reference equation 2.52
Reference equation 2.46
Reference equation
ANSWER:
a.)
Step 1 of 2
We have express the work done by electrostatic forces, in terms of the field , and the area of the plates, in moving the plates of a parallel-plate capacitor closer together by an infinitesimal distance .
The work done() by the electrostatic forces is given by the expression.
But
So,
Now, The pressure () is given by
Hence, The work done by the electrostatic forces is
Therefore, the work done by electrostatic forces, in terms of the field E, and the area of the plates, A is
b.)