# hw3sols - MasteringPhysics 10/8/08 7:07 PM Assignment...

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10/8/08 7:07 PM MasteringPhysics Page 1 of 11 http://session.masteringphysics.com/myct?productID=giancoli_up4 Assignment Display Mode: View Printable Answers Physys 202 Fall08 HW3 Due at 11:00pm on Wednesday, October 1, 2008 View Grading Details Capacitance: A Review Description: Multiple-choice questions on concept of capacitance. Use after Introduction to Capacitance. Some questions are repetitions of those in other problems. This fact may get some students frustrated. Learning Goal: To review the meaning of capacitance and ways of changing the capacitance of a parallel-plate capacitor. Capacitance is one of the central concepts in electrostatics. Understanding its meaning and the difference between its definition and the ways of calculating capacitance can be challenging at first. This tutorial is meant to help you become more comfortable with capacitance. Recall the fundamental formula for capacitance: , where is the capacitance in farads, is the charge stored on the plates in coulombs, and is the potential difference (or voltage) between the plates. In the following problems it may help to keep in mind that the voltage is related to the strength of the electric field and the distance between the plates, , by . Part A What property of objects is best measured by their capacitance? ANSWER: the ability to conduct electric current the ability to distort an external electrostatic field the ability to store charge Capacitance is a measure of the ability of a system of two conductors to store electric charge and energy. It is defined as . This ratio remains constant as long as the system retains its geometry and the amount of dielectric does not change. Capacitors are special devices designed to combine a large capacitance with a small size. However, any pair of conductors separated by a dielectric (or vacuum) has some capacitance. Even an isolated electrode has a small capacitance. That is, if a charge is placed on it, its potential with respect to ground would change, and the ratio is its capacitance . Part B Consider an air-filled charged capacitor. How can its capacitance be increased? Hint B.1 What does capacitance depend on? Capacitance depends on the inherent properties of the system of conductors, such as its geometry and the presence of dielectric, not on the charge placed on the conductors. Specifically, capacitance depends on the area of the conducting plates and the distance between the plates and is given by , where is a constant called the permittivity of free space. ANSWER: Increase the charge on the capacitor. Decrease the charge on the capacitor. Increase the spacing between the plates of the capacitor. Decrease the spacing between the plates of the capacitor. Increase the length of the wires leading to the capacitor plates.

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## This note was uploaded on 11/02/2009 for the course MASTERING PHYS taught by Professor All during the Spring '09 term at Kettering.

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hw3sols - MasteringPhysics 10/8/08 7:07 PM Assignment...

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