GEOLOGY

Detailed explanation-1: -On reversing the direction of current in a wire, the polarity of the faces of the wire also reverses. Thus, the direction of magnetic field produced by it also gets reversed and the correct choice is (a).

Detailed explanation-2: -The magnetic field generated is always perpendicular to the direction of the current and parallel to the solenoid. Hence if we reverse the current the direction of magnetic field also reverses.

Detailed explanation-3: -The change in the direction of current in a wire does not change the direction of magnetic field.

Detailed explanation-4: -If both current and magnetic field were reversed simultaneously, the direction of rotation would remain unchanged.

Detailed explanation-5: -We can change the direction of magnetic field around the circular current carrying wire by simply changing the direction of current opposite to the direction of current flowing earlier.