Here's why:

* Right-Hand Rule: The direction of the force on a current-carrying conductor in a magnetic field is determined by the right-hand rule. This rule states that if you point your thumb in the direction of the current and your fingers in the direction of the magnetic field, the force on the conductor will be in the direction of your palm.

* Current Reversal: When you reverse the direction of the current, you essentially flip your thumb in the opposite direction. This, in turn, flips the direction of your palm, resulting in a reversal of the force direction.

In summary: Reversing the current direction in a magnetic field causes the force on the conductor to reverse its direction. This is a fundamental concept in electromagnetism and has important applications in motors, generators, and other electrical devices.