Alternating Current
This is known as a direct current or DC. The two major types of currents are AC (alternating current) and DC (direct current). In AC the charges move back and forth, but in DC the charges flow in JUST ONE DIRECTION. Due to this characteristic it will not reverse direction like AC can.
Direct current does not reverse direction
direct current
You can reverse the direction of the magnetic field by reversing the direction of the electrical current.
Direct current (DC) is the term used to refer to current that flows in one direction and does not reverse its direction. This is in contrast to alternating current (AC), which changes direction periodically.
You can reverse the direction of a magnetic field by changing the direction of the electric current flowing through a conductor. This is known as the right-hand rule - if you pass your right-hand thumb in the direction of the current flow, your fingers will curl in the direction of the magnetic field. By reversing the direction of the current, you can reverse the direction of the magnetic field.
To reverse the direction of current in a motor, the current conducting wires must be switched. By changing the configuration of the wires, the flow of current through the motor's coils can be reversed, thereby changing the direction of rotation of the motor.
direct current
Direct current (DC) does not reverse its direction of flow. This means that the flow of electrical charge in a DC circuit always moves in one direction, from the positive terminal to the negative terminal.
Alternating current would fit this description.
Cooling fans use electric motors which operate by magnetism. As the direction of the current flow reverse, the magnetic poles reverse and hence the change in direction.
The magnetic field reverses direction.