# I don't understand electric fields.

silenzer
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?

## Answers and Replies

Legaldose
They just define it that way to say that the charge q is small enough not to affect the electric field already in place. If the electric field generated by q was comparable to E, then they would interact differently than they do in this situation.

anubhab92
yes.he is correct. furthermore,for proper studies an extra factor which is proportional to 1by r may arise..due to the disturbace by photon on the charge particle..