Chapter 4. Energy and Potential

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1 Chapter 4. Energy and Potential
Energy Expanded in Moving A Point Charge in An Electric Field The Electric Field Intensity: The force on a unit test charge If we attempt to move the test charge against the electric field, we have to exert a force equal and opposite to that exerted by the field.→Work!! 목원대학교 전자정보통신공학부 전자기학

2 The Line Integral 목원대학교 전자정보통신공학부 전자기학

3 Definition of Potential Difference and Potential
Work done by an external source in moving a charge Q Define Potential Difference V as the work done moving a unit positive charge from one point to another in an electric From the line-charge example A point charge 목원대학교 전자정보통신공학부 전자기학

4 The Potential Field of a Point Charge
The potential difference between two points in the field of a point charge depends only on the distance of each point from the charge and does not depend on the particular path used to carry out our unit charge from one point to the other. Let V=0 at infinity. Equipotential surface: a surface composed of all those points having the same value of potential. 목원대학교 전자정보통신공학부 전자기학

5 The Potential Field of a System of Charges: Conservative Property
목원대학교 전자정보통신공학부 전자기학

6 The potential is independent of path chosen between those two points.
Any field that satisfies an equation of the above form: conservative field 목원대학교 전자정보통신공학부 전자기학

7 Potential Gradient The magnitude of the electric field intensity is given by the maximum value of the rate of change of potential with distance. The direction of E is opposite to the direction in which the potential is increasing the most rapidly. 목원대학교 전자정보통신공학부 전자기학

8 The gradient shows the maximum space rate of change of a scalar quantity and the direction in which this maximum occurs. 목원대학교 전자정보통신공학부 전자기학

9 The Dipole Two point charges of equal magnitude and opposite sign , separated by a distance which is small compared to the distance to the point P at which we want to know the electric and potential fields. 목원대학교 전자정보통신공학부 전자기학

10 목원대학교 전자정보통신공학부 전자기학

11 Energy Density in the Electrostatic Field
목원대학교 전자정보통신공학부 전자기학

12 목원대학교 전자정보통신공학부 전자기학

13 The energy stored in the electrostatic field of a section of a coaxial cable or capacitor of length L 목원대학교 전자정보통신공학부 전자기학