Ques. How are the poles designated?
Ans. They are called the north pole and the south pole.
Ques. What is the distinguishing feature of each?
Ans. The north pole points approximately to the earth’s geographical north, while the south pole of a magnet points approximately to the earth’s geographical south.
The north pole is the positive (+) pole and the south pole is the negative. The north and south poles were formerly called in France, the austral and boreal poles respectively.
Magnetic Field.—When a straight bar magnet is held under a piece of card board upon which iron filings are sprinkled, the filings will arrange themselves in curved lines radiating from the poles. If a horse shoe magnet be held at right angles to the plane of the card board, the filings will arrange themselves in curved lines, as shown in fig. 108. These lines are called magnetic lines of force or simply lines of force; they show that the medium surrounding a magnet is in a state of stress, the space so affected being called the magnetic field.
Ques. What is the extent and character of the magnetic field?