8/4/08Lecture 1 Part 11 Electricity, Magnetism, and Fields Prof. Daniel Stump Lecture Notes:

8/4/08Lecture 1 Part 12 Field Theory Electricity 전기 Michael FaradayJames Clerk Maxwell The force on an electric charge is caused by a field, E(x). Electric Charge and Electric Field —electricity— 장의 이론

8/4/08Lecture 1 Part 13 Example: The electric field outside a charged sphere What is electric charge? Charge is a property of subatomic particles (electrons and protons) which creates the interaction with an electric field. Interactions of particles and fields E(x) and { q 1 q 2 q 3 … }  E exerts a force on each q i  Each q i adds to E(x) … that is “Field Theory”

8/4/08Lecture 1 Part 14 The Interaction between Particles (+,-) and the Electric Field

8/4/08Lecture 1 Part 15 Potential energy — Electric potential — Voltage units: … newton … joule = N m … volt = J/C Force Potential energy Electric potential

8/4/08Lecture 1 Part 16 Field Theory Electric field lines and equipotential surfaces HIGH potential (+) LOW potential (-)

8/4/08Lecture 1 Part 17 Electric field lines and equipotential surfaces. The equipotential surfaces are similar to contour lines on a topographic map. 지형 지도 —topographic map—

8/4/08Lecture 1 Part 18 Topographic Map contour lines are equipotentials of gravitational potential energy 지형 지도 —topographic map—

8/4/08Lecture 1 Part 19 Field Theory Electric field lines and equipotential surfaces

8/4/08Lecture 1 Part 110

8/4/08Lecture 1 Part 111 NEC 1 farad capacitor

8/4/08Lecture 1 Part 112 Capacitors Cap. Equations Q = C V U = ½ Q V

8/4/08Lecture 1 Part 113 Electric Current The human race has created a remarkable technology based on electric current. (Thomas Edison patent for light bulb = 1880) Example 전류 + E  E

8/4/08Lecture 1 Part 114 Ohm’s Law Demonstration: The “marbles and nails model” of electrical resistance to current. Why is the mean electron velocity constant as the electrons move to lower electric potential energy? I.e., the electrons do not accelerate, on average. Georg Ohm ( ) I = V/R (Ohm) Recall I = n e v A V v (voltage) (average electron velocity)