Final answer:
The direction of a resistance split phase motor's rotation can be altered by changing the connection on either the start or run winding, which modifies the magnetic field's phase relationship. Current reversal is achieved by brushes and a commutator, facilitating consistent rotation, while back emf produced during operation regulates the motor's speed.
Step-by-step explanation:
The direction of rotation of a resistance split phase motor can be changed by reversing the connection of either the start winding or the run winding but not both. This affects the phase relationship between the two windings, which determines the direction of the resulting magnetic field and thus the direction of motor rotation. When the motor starts, current flows through the wire loops placed within a magnetic field, which causes them to rotate. The current is systematically reversed using brushes and a commutator to maintain consistent torque and rotation.
In a direct current (DC) motor, this reversal happens every half-turn to keep the motor turning in the same direction. As the torque applied on the wire loop by the magnetic field rotates it to a position where brushes momentarily stop the current, no torque acts on the loop. However, the loop's momentum carries it to a point where the current is restored but flows in the opposite direction, beginning the cycle anew, as per Faraday's law and Lenz's law.
Back emf, also essential to motor operation, is generated due to the change in magnetic flux when the coil turns. It opposes the input emf, essentially acting as feedback that regulates the motor's speed, increasing when the motor speeds up and decreasing when it slows down.