Answer: The correct answer is "Its speed can be slowed".
Explanation:
The current carrying conductor produces the magnetic field. The electric current produces the magnetic field.
The motion of the charge produces the electric field and the magnetic field. If the charge is not moving then it will produce electric field only not magnetic field.
The rate of flow of charges constitutes the current. If the current is not flowing in the conductor then, the magnetic field will not produce. If the amount of current flow increases then the strength of the magnetic field increases.
The magnetic field can be produced by following methods from the given options :
It can be turned on and off.
Its direction can be reversed.
Its strength can be changed.
Therefore, the correct option is (d).
