question_answer 64)

  Why does a magnetic compass needle pointing north and south in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it? Describe some salient features of magnetic lines of field concept.

Answer:

                    When a magnetic compass needle pointing north and south in the absence of a nearly magnet or a current loop, it is acting upon by the earth's magnetic field only. But in the presence of a magnet or a current loop (which also has a magnetic field) the earth's magnetic field near the compass is modified and the needle is deflected from north and south directions. The salient features of magnetic field lines are (i) A magnetic field line is directed from north-pole to south-pole outside the magnet. (ii) A magnetic field line is a closed and continuous curve (iii) The magnetic field lines never intersect each other, because if two lines meet, it means that force is acting in two directions at that point which is not possible. (iv) Closer the field lines, stronger is the magnetic field and vice-versa is also true, Magnetic field lines are parallel and equidistant, those represent a uniform magnetic field.