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Explore the dynamics of electricity and magnetism, the interaction of matter and electromagnetic fields explained through Maxwell equations, the concept of electric field, and the Coulomb Force Law.
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Course Organization • Syllabus • Lesson Plan • Grading • Participation Bonus • Textbook (M&I II Electricity and Magnetism …) • Quest • i-Clickers (register on Quest)
What you need to remember from 303K • Vectors • How particles move and are affected by forces • Momentum: ; • Newton’s 2nd Law: • Work and Energy: Right Hand Rule
Clicker Question 1 and . What are and ?
Clicker Question 2 and . What is ? Recall: Use your results to find
Interaction of Matter and Electromagnetic Fields What will you learn? aurora borealis Backpacking in Alaska • Sun spits out Charged Particles (Solar Wind) • Earth’s Magnetic Field extends out into space and collects charged solar wind. • Charged particles are concentrated at poles • Collisions of these high velocity charges with air makes the light of the aurora
Maxwell equations: Lorentz force: More Mathematically … The interactions between matter and Electric and Magnetic fields can be explained with just a few equations.
Point Charges • Two types: positive and negative • Like charges: repel • Opposite charges: attract • Charge is quantized in units of e • Millikan’s oil drop experiment (1910-1913) • Point charge: Size is small compared to the distance between it and other objects of interest • Electric charge is an intrinsic property of the fundamental particles that everything is made of
Charles-Augustin de Coulomb (1736 - 1806) Q1 Q2 F F The Coulomb Force Law "The magnitude of the electrostatic force between two point charges is directly proportional to the magnitudes of each charge and inversely proportional to the square of the distance between the charges."
r + F21 r - + 2 + 2 F21 1 Force repulsive Force attractive 1 The Coulomb Force Law 0 = permittivity constant Force on “2” by “1”
Units and Constants SI units of electric charge: Coulomb, C Constants: 1/40 = 9x109 N.m2/C2 0 = 8.85x10-12 C2/N.m2 permittivity constant e = 1.602x10-19 C 1 C = 6.24x1018 elementary charges Particle Charge electron -e positron +e proton +e antiproton -e muon +e or –e pion +e or –e or 0 neutron 0
Structure of Atom Matter consists of atoms 1 cm3 : ~1024 atoms Nucleus: ~104 times smaller than electron cloud, ~104 times heavier than electron. 1Å=10-10m Example: nucleus of the iron atom Size: ~10–15 m, mass: ~10-25 kg Nucleus charge = +Ze, atom with Z electrons is neutral.
The Concept of Electric Field Accelerates at 9.8 m/s2 – why? Accelerates at 1011 m/s2 – why? There are many possible configurations of charges to produce the observed effect.
Electric Field There is something in space waiting for a charged particle to interact with it! This virtual force is called electric field. An electric field created by charge is present throughout space at all times, whether or not there is another charge around to feel its effect.
Force between Charges + The Electric field of the Point Charge Q q + Q Electrical Field is convenient tool turns out to be measurable … so really exists
+ Electric Field of Point Charge + Spherically Symmetric
Direction of Electric Field Points along Line Field Lines E Field Lines _ + Isolated Positive Charge Isolated Positive Charge + + Begin and End on Charges or Infinity; Never Cross
Homework on Quest: Ch14-h1; review Ch14-h0 • Read Ch14.1-14.8 • i-Clickers (register on Quest) Things to do _