question_answer 41)

  If the key in the arrangement as shown below is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are (a) Concentric circles                                                      (b) Elliptical in shape (c) Straight lines parallel to each other                    (d) Concentric circles near the point O but of elliptical shapes as we go away from it

Answer:

                  (c) When the key is taken out (the circuit is made open), no current flows through the wire hence, no magnetic field exists due to the conductor. The only magnetic field is due to Earth's magnetic field and is straight lines parallel to each other. Whose horizontal component is directed from geographical South to geographical North on the horizontal plane ABCD.