question_answer

A magnetic needle is placed on a cork floating in a still lake in the northern hemisphere. Does the needle together with the cork move towards the north of the lake?

A) Yes                                                        

B) No

C) May or may not move                  

D) Nothing can be said

Correct Answer: A

Solution :

Key Idea: Magnetic needle behaves as a dipole. Magnetic needle is a dipole which is in earth's uniform magnetic field and as a dipole in a uniform field does not experience any net force but may experience a couple as shown  in figure, so the needle together with the cork will not translate ie, move towards the north of the lake, but will rotate and set itself parallel to the field with its north pole pointing north.