 GAUSS'S LAW STUDY GUIDE AP LEARNING TARGETS TERMS: Test Charge: A mathematical construct-- a charge that does not exert any influence on surrounding particles but IS influenced by other electric fields. conductor - materials where electrons can roam insulator - materials that keep their electrons close to home coulomb - a unit of electrical charge (see below) CONSTANTS: e-mass = 9.1 x 10-31 kg charge of an electron = 1.60 x 10-19 coulombs (C) ke = 8.987 x 109 Nm2/C2 ke = 1/4πεo FORMULISTICS: Electrical Force: Fe = (keq1q2)/r2 Electrical Field: E = Fe / qo where qo  = a positive test charge E= (keq)/r2 Gauss's Law (for an object enclosing 1 or more charged particles) Φ = ∮E ∙A dA or ∮EAcosθ dA where θ is the angle between the electrical field line vector and the area vector Φ = qin/εo : the electric flux through an ENTIRE gaussian surface is equal to the algebraic sum of the charges INSIDE the surface divided by the permitivity of free space Generally: the more symetric the surface area of the gaussian surface the more accurate is this formula. CONCEPTS: What is an electric field? What are electric field lines? What is a test charge? What are the unique properties of a test charge and why are they important to keep in mind? What is a gaussian surface and why do we care? What is an area vector? What is the effect of presence or absence of charges inside a gaussian surface on any analysis of electric flux in and out of that surface? Why do we use the "dot" product of the area vector with the electric field vector when calculating electric flux? What is the effect of surface area symetry on any analysis of electric flux in and out of a gaussian surface? What is the effect of a uniform electric field on any anlysis of electric flux in and out of a gaussian surface? Mr Chase tells us (quite correctly by the by) that we can ALWAYS use: Φ = qin/εo to calculate the electric flux through a gaussian surface. What are the limitations to this approach and when does it work best?