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**Unformatted text preview: **Class 5 Electric Fields and Electric Potentials Physics 106 Fall 2011 Press CTRL-L to view as a slide show. Learning Outcomes You should know the following items from the last lesson: I The electric field is defined by E = F / q I The electric field points in the direction of the force on a small positive test charge I The electric field can be described by electric field lines I The electric field vector, ~ E , is tangent to the electric field lines at each point I Field lines are closer together where the field is stronger I Be able to draw the electric fields of simple arrangements of charges. I Know the characteristics of electric fields near conductors I Work standard problems involving the electric field. Learning Outcomes Today we will consider: I What is the electric potential? I How are the electric field and the electric potential related? I How can we find the electric field and the electric potential? I How are electric fields and electric potentials used in practical applications? I The elecric potential is the potential energy divided by the charge I The electric potential is also called the voltage I Applying fields to a CRT Electric Field Line Patterns I Point charge I The lines radiate equally in all directions I For a positive source charge, the lines will radiate outward Note how the lines naturally get farther apart at larger distances from the source. Electric Field Line Patterns I For a negative source charge, the lines will point inward Electric Field Line Patterns I All the lines start on positive charges and end on negative charges. I The electric field is strong between the charges. I The field is weak far from the charges. Electric Field Line Patterns I Far from the charges, the field looks like one charge of 2q. I The field is weak between the charges. Conductors in Electrostatic Equilibrium I E inside is zero I Charge moves to the surface I E is perpendicular to the surface I Charge collects at pointed spots and the field is larger there Electric Fields of Objects E Fields of Selected Objects In some very special cases we can use symmetry to help find electric fields. Electric Field of a Point Charge Coulombs law tells us: E = k e Q r 2 E = Q 4 r 2 Electric Field of a Charged Sphere The electrical field outside a uniformly charged spherical shell is the same as that of a point charge....

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