16 Unit III On-a-Page

Instructor’s Note

This chapter very strongly follows the ideas of a few distinct discussed in Unit I On-a-Page.



Electric fields, forces, potentials, and potential energies from a positive point charge.
This image effectively summarizes the connections between the two new ideas in this chapter, electric fields and electric potentials, as well as showing how they connect to ideas with which you are already familiar: forces and potential energy.
  • All charges generate electric fields  \vec{E} (units N/C orV/m)
  • For a point charge \vert \vec{E} \vert = \frac{1}{4 \pi \varepsilon_0}  \frac{q}{r^2}
  • Point away from positive, towards negative
  • These are real and exist regardless if something is there to feel or not!
  • Put a charge in an electric field ⇒ it will feel a force \vec {F } =q \vec {E}
  • Can also think in terms of energy: All charges generate electric potentials V (units Volts)
  • For a point charge V = \frac{1}{4 \pi \varepsilon_0} \frac{q}{r}
  • Exists if something is there to feel or not!
  • Put a charge in a potential it has a potential energy U = qV
  • Electric potentials and electric fields are two sides of the same coin
  • Just like in P131: Can think of forces or energy
  • \vec{E} points ‘down the potential hill’
  •  \vec{E} = - \frac{\Delta V} {\Delta x}



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Physics 132: What is an Electron? What is Light? by Roger Hinrichs, Paul Peter Urone, Paul Flowers, Edward J. Neth, William R. Robinson, Klaus Theopold, Richard Langley, Julianne Zedalis, John Eggebrecht, and E.F. Redish is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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