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Physics 52 Midterm 2 Study Guide(7)_2

# Physics 52 Midterm 2 Study Guide(7)_2 - Physics 52"Study...

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Physics 52 "Study Guide" for Midterm #2 ("Laundry List" of important concepts) Todd Sauke Concept (important concepts in bold; vectors also shown in bold ) Symbol or Equation Prerequisites: Physics quantities are typ. either scalars or vectors (magnitude & direction) components of vectors add From mechanics , total external force on a body = mass x acceleration Σ F ext = m a (SI newton, "N") Mass (SI kilogram, "kg") resists change in motion (via " momentum" , p ) p = m v , F ext = d p /dt A moving mass has energy of motion, " Kinetic Energy " (SI joule, "J") KE = ½ m v 2 (a scalar) Electric Charge is conserved, quantized, comes in "positive" and "negative" e = 1.602 x 10 -19 C Like charges repel ( radially ); opposite charges attract; Coulomb's Law F = (1/(4 π ε 0 )) q 1 q 2 / r 2 All "normal" matter is made up of protons, neutrons and electrons m p = 1.67 x 10 -27 kg Protons have +e charge; electrons have –e. Their mutual attraction holds m e = 9.11 x 10 -31 kg everything together. In a conductor, electrons are free to move around. For materials obeying Ohm's Law , current is proportional to voltage V = I R R = resistance Maxwell's Equations show that Light is an Electromagnetic wave c = 1/ ε 0 μ 0 = 2.998 x 10 8 m/s Electromagnetic waves are transverse w/ E , B to each other and propagation E(x,t ) = E max cos(kx- ω t) "k" is the wave number of a propagating sinusoidal electromagnetic wave k = 2 π / λ E max = c B max There are two possible polarizations of light for x-propagation ( E in y or E in z) (or tilted in y-z plane) For an electromagnetic wave traveling in a dielectric (eg. glass) v < c v 2 = 1 / ( ε μ ) = c 2 / K K m K is called the dielectric constant of a medium. K m is relative permeability . K m ~ 1.00 for most dielectrics Visible light is but a small part of the spectrum of electromagnetic waves λ xray < λ uv < λ vis < λ ir < λ μ wav < λ tv Light and Optics: Light waves typically appear to travel in straight lines called light rays . Because of the way that light forms shadows and appears to travel in rays, people were led to think of light as a stream of particles. But then wave properties (of very short wavelength) were noticed and light became recognized as a wave. λ vis ~ 400 – 700 x 10 -9 m Light has both wave and particle properties. Light propagates as a wave. Maxwell's Equations Æ light is generated (emitted) by accelerating electric charges When light interacts with matter, it is emitted or absorbed in "packets" of Quantum mechanics energy called photons . This packet aspect of light gives it a particle nature. (another course of study) In this course, we (mostly) confine our study of light to its wave nature. Light rays are a graphical tool Light rays are drawn perpendicular to the wavefronts of a light wave. θ

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Physics 52 Midterm 2 Study Guide(7)_2 - Physics 52"Study...

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