Physics 17: 1-6 Electric Potential

Homework

Reading Preparation
Key Equations
WebLecture
Study Activity
Chat Preparation Activities
Chapter Quiz
Lab Work

Reading Preparation

Text Reading: Giancoli, Physics - Principles with Applications, Chapter 17: Sections 1 to 6

Study Points

17.1: Electric potential V = PE/q is a measure of the work done to move a charge q from infinity to a particular spot in an electrical field. We can expand this to the concept of potential difference, the change in the field potential as we move the point charge from one position to another in the field.
17.2: An electrical field can be measured as newtons per Coulomb (force required to move a charge) or by volts per meter (difference in potential over a given distance) E = -V/d = qW/d = q (V₂-V₁)/d.
17.3: In any field, we can map the points of equipotential (where V is the same value). Moving a charge along an equipotential line requires no work. (Compare this to moving a mass along a level, frictionless surface.)
17.4: We measure the work done in moving across potentials as volt.
17.5: The potential due to a point charge varies as distance from the charge changes, V = kQ/r = (1/4πε₀)(Q/r). Here ε₀ is the permittivity of charge in a vacuum. It will vary with the medium of the field.
17.6: The potential due to a dipole (two opposite charges, close together) varies as the inverse square of the distance to the center of the dipole.

Key Equations

Work in an electric field: $W = Fd = qEd$
Potential difference between two points in an electric field $Δ PE = - qED = - W$
Electric potential at a single point $V_{a} = \frac{{PE}_{a}}{q}$
Electric potential between two points $Δ V = \frac{{PE}_{b} - {PE}_{a}}{q} = \frac{- W}{q}$
Electric field and electric potential $E = \frac{- Δ V}{d}$
Point charge electric potential $V = k \frac{Q}{R} = \frac{1}{4 π ϵ_{0}} \frac{Q}{R}$
Dipole Potential at r from field due to two particles with equal but opposite charge Q separated by distance l $V \approx \frac{kp \cos θ}{r^{2}} where p = dipole moment = Ql$

Web Lecture

Read the following weblecture before chat: Electric Potential

Study Activity

Return to the charges and fields lab. This time, use the simulation to explore how voltages vary as you introduce new charges and move them around. Turn on the grid so that you can precisely place charges. Use the sensors to display net field direction and force values along with voltages at specific points. What is the potential difference (voltage) when you

Place a +10 nC primary charge at the center of the display and add a +1 nC test charge one space unit (5 small units) away?
Place a +10 nC primary charge at the center of the display and add a -1 nC test charge one space unit (5 small units) away?
What happens if you double the primary charge?
Place a +1 nC charge and a -1 nC charge 1 small unit apart and use the sensor to measure the dipole field around the two charges.

Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.

Chat Preparation Activities

Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

The chapter quiz is not yet due.

Lab Work

If you want lab credit for this course, you must complete at least 18 labs; you may complete more if you are preparing for the AP exam.. One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!

Lab Instructions: Circuits I

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Physics

Chapter 17: 1-6