Chapter 21.1, Problem 20SSC

To determine

Whether the test is small enough to give accurate result.

Explanation of Solution

Introduction:

A test charge is a charged object used to measure electric field. An ideal test charge should be infinitesimal such that it does not interfere with the other charges whose field is to be measured.

The given test charge is not very small so that it will measure the electric field of two given negative unit charges. It will disturb the field produced with its own field; hence, the measurement will be inaccurate.