question_answer 22)

A compass needle free to turn in a horizon plane is placed at the centre of circular coil of 30 turns and radius 12 cm. The coil is in a vertical plane making an angle of with the magnetic meridian. When the current in the coil is 0.35 A, the needle points west to east.                 (a) Determine the horizontal component of the earth?s magnetic field at the location.                 (b) The current in the coil is reversed, and the coil is rotated about its vertical axis by an angle of in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the place to be zero.  

Answer:

                (a) Using we get                                                                 (b) The compass needle will point east to west i.e. it reverses from its original direction.