Main Question or Discussion Point
According to my textbook, the electrical field is defined as E = F/q where q --> 0, because we want the test charge to affect the other charges around it in the least possible way. It then goes on to say that qE = F is true for charges not strong enough to move the other charges. Why is that, if the electrical field was defined very specifically? Why can I use qE = F for all charges, as if the q wasn't a test charge all along?