Overview
This lecture explains how electric motors work using the motor effect, and details how a split ring commutator ensures continuous rotation.
The Motor Effect
- A current-carrying wire in a magnetic field experiences a force; this is called the motor effect.
- The force’s direction depends on both the current direction and the magnetic field direction.
- Fleming’s left hand rule is used to determine the direction of this force.
Forces on a Coil
- If two wires have opposite current directions in the same magnetic field, they experience forces in opposite directions.
- Connecting the wires forms a coil, with current flowing in from one terminal and out the other.
- One side of the coil experiences an upward force, and the other side a downward force, making the coil spin.
The Need for a Split Ring Commutator
- After a 180° turn, the current in the coil reverses direction, making the coil want to flip back, not complete full rotations.
- To maintain rotation in the same direction, the current direction must switch every half turn.
How the Split Ring Commutator Works
- The split ring commutator swaps the positive and negative connections to the coil every half turn.
- This ensures the force direction on the coil’s sides remains constant, allowing continuous rotation in one direction.
- The positive and negative terminals remain stationary, while the commutator rotates with the coil.
Increasing Motor Power
- Motor speed can be increased by increasing the current through the wire.
- Adding more turns to the coil increases the motor's power.
- Using stronger magnets raises the magnetic flux density, boosting motor performance.
Key Terms & Definitions
- Motor Effect — The force experienced by a current-carrying wire in a magnetic field.
- Fleming’s Left Hand Rule — A rule to determine the direction of force, magnetic field, and current in a motor.
- Split Ring Commutator — A device that reverses the current in a coil every half turn to ensure continuous motor rotation.
- Magnetic Flux Density — A measure of the strength of the magnetic field.
Action Items / Next Steps
- Review Fleming’s left hand rule and practice applying it to different wire and field directions.
- Learn to label parts of a simple electric motor diagram, including the split ring commutator.