1. PHYS 221 Recitation Kevin Ralphs 20 June 2014

2. Overview Work-Energy Theorem with Electric Forces Potential Equipotential Lines and Surfaces

3. Potential Energy Situational: Assumes uniform electric field and straight path Situational

4. Potential Situational: Assumes an irrotational electric field

5. Potential Situational Assumes an irrotational electric field Situational:

6. Potential (Calculus Detour)

7. Equipotential Lines and Surface Equipotential lines and surfaces are the lines and surfaces that have the same value of potential It’s an alternate way of viewing the field and is analogous to contour maps for altitude which are approximately isolines for the gravitational potential Denser lines indicate a stronger field Positive charges move UP potential while negative charges move DOWN potential

8. Potential Word of caution: – Potential is not the same as potential energy, but they are intimately related – Electrostatic potential energy is not the same as potential energy of a particle. The former is the work to construct the entire configuration, while the later is the work required to bring that one particle in from infinity – There is no physical meaning to a potential, only difference in potential matter. This means that you can assign any point as a reference point for the potential – The potential must be continuous; otherwise we would have undefined electric fields

9. Tying it Together Electric Field Change in Potential Change in PE Electric Force Multiply by q Multiply by -Δx Vectors Scalars

10. Analogies with Gravity Electricity and magnetism can feel very abstract because we don’t usually recognize how much we interact with these forces There are many similarities between gravitational and electric forces The major difference is that the electric force can be repulsive Gravity even has a version of Gauss’s law ChargeForceFieldPE Electricityq Gravitym