I am quite confused about the motor rule. I have a few questions concerning the topic: 1. How can I determine the direction of magnetic field acting on a current-carrying conductor? 2. How can I use the left-hand rule practically? Suppose that the current is in the north direction, and the magnetic field points south-west, how can I suppose to use the motor rule to predict the direction of the magnetic force? I can control my fingers to bend that way! What are the secrets behind this rule? Is it a MUST that we use the thumb to represent force alone, but not the other two fingers? Thanks a lot.