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Physics Lesson Plan Teacher Howard Unit Title Length Goal(s)/PLO(s): Course Grade Level Block/Period J3 calculate electric potential energy and change in electric potential energy define electric potential energy and change in electric potential energy solve problems that deal with two point charges at rest and that involve – electric potential energy – charge – distance of separation Phys 12 12 Date Class Size Lesson #, of 17-01 solve problems that deal with two point charges where one is moved and that involve – change in electric potential energy – distance of separation (initial and final) – charge Materials: Timeline Class Activities Introduction Body Notes 17-01…17-04 Closure Questions 1-10, 12-13, Problems1-13 odd 17-01 Electric Potential Energy and Potential Difference Electric potential energy is a conservative force • The work done by the electrostatic force depends on position of particles, not the paths taken The change in potential energy between two points (a and b) is equal to the negative work done to move the object from a to b. ∆PE = -W If we move a positive point charge within a uniform electric field (like between two charged plates) then W = Fd =qEd The change in electric potential energy is the negative of the work done by the electric force PE b -PE a =-qEd Electric potential energy decreases. Energy is conserved and the kinetic energy increases. Electric Potential The electric potential energy per unit charge Only differences in potential energy have any physical meaning Potential Difference • The difference in electric potential from point a to b • The negative of the work done by the electric field to move a charge from a to b or from your data book The unit of electric potential is the joules/coulomb or the Volt (V) Remember that we must define a zero point for potential energy, and it is the changes that matter. • The ground (earth) is usually defined as zero Example 17-1 You can use gravity analogies to understand how different positions result in different potentials • Keep in mind that there are two types of charge so moving a positive charge from a to b will give the opposite ∆V as moving a negative charge Batteries and generators are designed to maintain a constant potential difference and different devices draw different amounts of charge. Example 17-2 17-02 Relation between Electric Potential and Electric Field For a uniform electric field (between 2 charged plates) the work done to move a positive charge is equal to the negative change in potential energy. W=-PE=-q∆V and W=Fd=qEd -q∆V = qEd ∆V = -Ed • your sheet omits the negative sign Example 17-3 17-3 Equipotential Lines Equipotential lines can be drawn to represent the electric potential. charges-and-fields_en.jar • Equipotential lines and electric field lines are perpendicular • E points to lower values of V • Equipotential lines are continuous (no start or end) 17-04 Electric potential Due to Point Charges When dealing with small numbers of electrons, protons or molecules, joules are too big a unit. Electron volt (eV) The energy acquired by a particle carrying a charge whose magnitude equals that on the electron (q=e) as a result of moving through a potential difference of 1V ∆PE=qV 1eV=(1.6E-19C)(1.0V)=1.6E-19 J • The eV is not a proper SI unit and should not be used in your calculations o Convert to Joules first Questions 1-10, 12-13 Problems1-13 odd