Hidden Charges

Overview

An electric field is a vector field; that is, at every point of space it has both a magnitude and a direction. In this exercise you will explore the electric field produced by a number of point-like charged particles. However, you won't be able to see the charges or draw field lines.

The program displays a rectangular area that contains some hidden charges. When you place the mouse cursor in the rectangular area, the program gives some information about the electric field due to the charges. An arrow appears with one end on the cursor. Think of the arrow as a vector that represents the electric field at the point of the cursor. The direction of the arrow gives the direction of the electric field, and its length indicates the strength of the electric field (it's not proportional!). Use the cursor to explore the area containing the charges, and then answer the questions that follow.

Questions

  1. How many charges are in the rectangular area?




  2. Give the coordinates and sign of each charge. The coordinates of the point where the cursor is located appear in the browser's status line at the bottom of the window. If you manage to put the cursor directly on a charge, the arrow will disappear, and a small circle will appear there.



  3. At how many points in the area is the electric field equal to zero?



  4. Give the coordinates of those points where E = 0.



  5. Rank the charges according to their charges, most positive first. (The location of the points where E = 0 should help here.)




Copyright 1998-1999 Rensselaer Polytechnic Institute. All Rights Reserved.