Understanding Electric Potential and Electric Potential Energy, Study notes of Physics

Download Understanding Electric Potential and Electric Potential Energy and more Study notes Physics in PDF only on Docsity! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Chapter 29. The Electric Potential At any time, millions of light bulbs are transforming electric energy into light and thermal energy. Just as electric fields allowed us to understand electric forces, Electric Potential allows us to understand electric energy. Chapter Goal: To calculate and use the electric potential and electric potential energy. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Lecture 5.2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. What are the units of potential difference? A. Amperes B. Potentiometers C. Farads D. Volts E. Henrys Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. What are the units of potential difference? A. Amperes B. Potentiometers C. Farads D. Volts E. Henrys Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. New units of the electric field were introduced in this chapter. They are: A. V/C. B. N/C. C. V/m. D. J/m2. E. /m. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. The electric potential inside a capacitor A. is constant. B. increases linearly from the negative to the positive plate. C. decreases linearly from the negative to the positive plate. D. decreases inversely with distance from the negative plate. E. decreases inversely with the square of the distance from the negative plate. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Chapter 29. Basic Content and Examples FIGURE 29.4 The electric field does work I. 7an\ols Spey up on the charged particle. y . 2. : ag , u The electric field does work on the Cnty, MHLW AEN particle. We can express the work as a change in electric potential energy. 3. Paoyy is Ceeonveth Electric field 4 . Whoa tery is foot 7 Au = W ="Gear try ee KG emencmerncenecin a Ar E ? ASa-— Av ee The particle is “falling” 4 in the direction of E. Aso d , dA A = +4 Ed$ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-WesleyA. A Ut —~ Uc = 9E-S Be Uo Flute field does work on Charge: —> ~-—> We F.ar = F. ar. Ose = Ky - Ky / (Chan qe f Kinetiz energy) — total en -keg 0 Nee g sbi Ktg | Cheetrie potemhal i$ Couseryed., Cne ry Paretl Blake Copact ts U Vy GES + in Bou lu nog itera Peale , C= Uz Us = 9 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Electric Potential Energy The electric potential energy of charge q in a uniform electric field is where s is measured from the negative plate and U0 is the potential energy at the negative plate (s = 0). It will often be convenient to choose U0 = 0, but the choice has no physical consequences because it doesn’t affect Uelec, the change in the electric potential energy. Only the change is significant. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. The Potential Energy of Point Charges Consider two point charges, q1 and q2, separated by a distance r. The electric potential energy is This is explicitly the energy of the system, not the energy of just q1 or q2. Note that the potential energy of two charged particles approaches zero as r . FIGURE 29.9 The potential-energy diagrams for two like charges and two opposite charges. (a) Like charges - approach for two like f charges with total : energy E, mech | Energy “tees Distance of closest | | | | | Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. FIGURE 29.9 The potential-energy diagrams for two like charges and two opposite charges. (b) Opposite charges 0 4— r E mech ‘Distance of maximum separation for two opposite charges Energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.  U.=O-. Ke = Ve ee Kf = 0 Up + Kt = “i doilu CH e—— ( / 2 2 ™% Ue Uc + Koz tmy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. EXAMPLE 29.2 Approaching a charged sphere Potential Energy of Multiple Point Charges é © 8 oO @ 9 6 6 Principle of linear superposition: ; . K 4g; | v=) i<g = Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. FIGURE 29.16 The energy of a dipole in an electric field. Turning points for Energy — Unstable oscillation with equilibrium energy Beet at p a +180° a \ oe —¢ I Oo | Oo 0 180 Enos or Stable equilibrium at d = 0° Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. The Electric Potential We define the electric potential V (or, for brevity, just the potential) as Charge q is used as a probe (test charge) to determine the electric potential, but the value of V is independent of q. The electric potential, like the electric field, is a property of the source charges. The unit of electric potential is the joule per coulomb, which is called the volt V: Cledrc patewtiod MSide Capacita-