# SJSU EE 140 - ch23_Electric_Potential (18 pages)

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## ch23_Electric_Potential

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- Pages:
- 18
- School:
- San Jose State University
- Course:
- Ee 140 - Principles of Electromagnetic Fields

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Chapter 23 Electric Potential Dr Ray Kwok SJSU Electric Potential Dr Ray Kwok Goals for Chapter 23 To study and calculate electrical potential energy To define and study examples of electric potential To trace regions of equal potential as equipotential surfaces To find the electric field from electrical potential Electric Potential Dr Ray Kwok Electrical Potential Energy m1m 2 FG G 2 r q1q 2 Fe k 2 r Gravitational force Coulomb force similar to gravitational electrostatic force is a conservative r r force Wnet F d l 0 which means there is a potential energy associated with this force such that F dU dx or gradient in 3D Electric Potential Dr Ray Kwok Work and Potential Energy There is a uniform field between the two plates As the charge moves from A to B work is done on it W Fd q Ex xf xi PE W q Ex x Only for a uniform field Electric Potential Dr Ray Kwok Potential Difference voltage Potential difference is not the same as potential energy The potential energy and the potential difference are related by PE q V Both electric potential energy and potential difference are scalar quantities Units of potential difference V J C A special case occurs when there is a uniform electric field V VB VA Ex x Gives more information about units N C V m Electric Potential Dr Ray Kwok Equipotential Contour 2D On a contour map the curves mark constant elevation the steepest slope is perpendicular to the curves The closer together the curves the steeper the slope Electric Potential Dr Ray Kwok Equipotential Surfaces 3D An equipotential surface is a surface on which all points are at the same potential No work is required to move a charge at a constant speed on an equipotential surface The electric field at every point on an equipotential surface is perpendicular to the surface Electric Potential Dr Ray Kwok Equipotentials and Electric Fields Lines Positive Charge The equipotentials for a point charge are a family of spheres centered on the point charge The field lines are perpendicular to the electric potential at all points Electric Potential Dr Ray Kwok For two point charges Electric Potential Dr Ray Kwok Application Electrostatic Precipitator It is used to remove particulate matter from combustion gases Reduces air pollution Can eliminate approximately 90 by mass of the ash and dust from smoke Recovers metal oxides from the stack Electric Potential Dr Ray Kwok Electric Potential of Point Charges The difference in potential energy between points A and B is r r B q oq W F d r k 2 dr r A U k q oq qq k o rB rA U B U A k q oq qq k o rB rA q oq q oq UA UB k k rA rB Electric Potential Dr Ray Kwok The Electric Potential of a Point Charge PE between 2 pt charges Electric potential from 1 pt charge q1q 2 r q V k r U k shown here is V for a positive and negative charge Electric Potential Dr Ray Kwok Potential energy curves PE versus r q1q 2 U k r U 0 for like charges U 0 for opposite charges F dU dr Electric Potential Dr Ray Kwok The Electric Potential of Point Charges The electric potential of a group of point charges is the algebraic sum of the potentials of each charge Electric Potential Dr Ray Kwok Human a complex circuit An electrocardiograph plots the heart s electric potential ECG Electric Potential Dr Ray Kwok EEG An electroencephalograph measures the electrical activity of the brain Electric Potential Dr Ray Kwok The Electron Volt The electron volt eV is defined as the energy that an electron gains when accelerated through a potential difference of 1 V Electrons in normal atoms have energies of 10 s of eV Excited electrons have energies of 1000 s of eV High energy gamma rays have energies of millions of eV 1 eV 1 6 x 10 19 J Electric Potential Dr Ray Kwok Example

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