I think I understand how signals can be sent by field disturbances, and that the disturbance is propogated at the speed of light. Now, I was wondering about the case where a stationary field is already set up and you place a test charge in that field. Does that charge move instantaneously or is there a time interval (equal to d/c, where d = distance to field origin) between the placement and the motion? My intuition tells me that the motion must be instantaneous because the field is already set up at that location. Am I correct? Thanks.