5.4 Electric energy, Electric Potential, and Electric Potential Difference p Electric Potential Energy In Uniform Fields The Work-Energy theorem states that work done on an object is equal to the change in object’s energy. W = ΔE p This equation applies to all types of energy including gravitational potential energy and electric potential energy. In both cases lines of force show the direction that either a massive object or a charged object would move do to the gravitational or electric field.

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Field, Energy and Charges: p. 189 The positive charge would gain electric potential energy as it moves from position A to position B. Of course a negative charge would gain electric potential energy as it moved form position B to position A. When a positive charge spontaneously moves from position B to position A, it loses electric potential energy and gain kinetic energy (it will increase its speed) very much like a falling object.

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Potential Energy of Multiple Charges – Non-Uniform Field p Potential energy must be specified to a reference location. For electric potential energy we use distance set to infinity to set electric potential energy to zero at this point F e = k Q 1 Q 2 r2r2 And since : W =F e x d W = E p = k Q 1 Q 2 r2r2 x d E p = k Q 1 Q 2 r (and d = r)

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Potential Energy of Multiple Charges – Non-Uniform Field p. 192 Determining the work done in moving a charge is accomplished by calculating the change in potential energy. For example :A charge Q 1 is moved form d 1 to d 2 relative to charge Q 2. Q1Q1 Q2Q2 d1d1 d2d2 W = ΔE p = k Q 1 Q 2 d2d2 d1d1 - To calculate the work done:

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Potential – It’s all about location p. 193 Electric potential is defined as the amount of work (energy) required to move a unit charge to a point in an electric field. Units: 1 Volt = 1 Joule/coulomb V = Q ΔEpΔEp Electric potential is used to express the effect of a source’s electric field in terms of location within the electric field. Electric potential is a property of the location of a charge within an electric field, and not of the amount of charge.

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Potential of Single Point Charges p. 194 V = Q ΔEpΔEp To calculate the electric potential at some distance from a point charge: k Q 1 Q 2 Q r = Cancelling out one of the charges leave you with: V = k Q r P Q r

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electric Potential Difference p V AB = To calculate the electric potential difference or Voltage as a charge moves in an electric field: Q ΔE pB Q ΔE pA V AB = Q W AB The potential difference (V) between two points is defined as the amount of work required to move a unit of positive charge from the point that is lower potential to the point that is at the higher potential. (W AB = ΔE pB – ΔE pA )

5.4 Electric energy, Electric Potential, and Electric Potential Difference Electron Volt p. 196 On the atomic scale the Joule is a very large amount of energy. A smaller unit of energy, the electron volt (eV) is used. -+ electron 1 eV is the energy gained when 1 electron is accelerated by a potential difference of 1 volt. 1 eV = 1.6 x J

5.4 Electric energy, Electric Potential, and Electric Potential Difference Key Questions In this section, you should understand how to solve the following key questions. Page 189 – Quick Check #2 Page 191 – Practice Problem 5.4.1: #1 & 2 Page 195 – Quick Check #2 Page 196 – Practice Problem 5.4.2: #3 Page 197 – Practice Problem 5.4.3: #2 Page – Review 5.4 #2,4,6,8, 12 & 13