QUESTIONS IN THE BOX:


2. "Please explain the clockwise motion and counter-clockwise motion for positive and negative flux."

I think what the questioner wants to know is the relationship between the direction of the magnetic field in a coil and the electric current. What I can do is review the "rules" that might help you to determine the field direction.

Above I have sketched the situation for a solenoid carrying a steady current. Below, I have sketched the field directions, etc. you would "see" if you looked at (a) the left-hand end of the coil, and (b) the right-hand end.

From the drawings you can see that the magnetic field is directed "out" from the left-hand end and "in" at the right hand-end of the solenoid. We can determine the field direction relative to the current by using the right hand rule; when the current is counter-clockwise as in (a) the field is directed out of the page (just like the direction a screw moves when you turn it ccw, i.e., undo it). When you look at the right hand end of the coil, the current now appears to be traveling clockwise as in (b). Hence, by the right hand rule, the magnetic field is directed into the page.

The solenoid acts just like a regular permanent bar magnet ... so it has a "north end" and a "south end". You can determine the polarity of the ends of the solenoid by using the method taught to me by my physics teacher in high school in England over 40 years ago! Just draw the letters "N" and "S" with arrows on the ends as I've done. By aligning the arrows with the current direction you can tell which is the north end and which is the south end!

Back to the list of questions.