The close relationship between electricity and magnetism culminates in the motor effect, a fundamental principle that explains how electric motors convert electrical energy into mechanical energy (motion).

The motor effect states that a current-carrying conductor experiences a force when it is placed within an external magnetic field.

1. Magnetic Field of the Wire: We've learned that a current flowing through a wire creates its own magnetic field around the wire.
2. Interaction of Fields: When this current-carrying wire is placed in an external magnetic field (e.g., produced by a permanent magnet or another electromagnet), the magnetic field of the wire interacts with the external magnetic field.
3. Resultant Force: This interaction leads to a resultant force acting on the wire. This force pushes the wire.
4. Direction of Force: The direction of the force is crucial. It is always perpendicular to both the direction of the current in the wire and the direction of the external magnetic field. A common mnemonic for remembering this relationship is Fleming's Left-Hand Rule (though not strictly required for Grade 9, it's an excellent visual aid: Thumb = Force/Motion, Forefinger = Field, Middle Finger = Current).

There must be an electric current flowing through a conductor.
The conductor must be placed within an external magnetic field.
The current and the magnetic field lines must not be parallel to each other. The maximum force occurs when they are perpendicular.

Key Components of a Simple DC Motor:
- Stator (Permanent Magnets): These are stationary magnets (or electromagnets) that provide the constant external magnetic field within which the coil rotates.
- Rotor (Armature/Coil): This is the rotating part of the motor. It typically consists of a rectangular coil of wire (the armature) wound around a soft iron core to enhance the magnetic field.
- Commutator: This is a crucial component that allows for continuous rotation. It's a split-ring device made of conducting segments, insulated from each other. Its function is to reverse the direction of the current in the coil every half rotation.
- Brushes: These are stationary carbon contacts that press against the rotating commutator segments. They provide the electrical connection, allowing current to flow from the external power supply to the rotating coil.
- DC Power Supply: Provides the direct current to power the motor.

How a Simple DC Motor Works (Step-by-Step Qualitative Process):
1. Initial Force: When direct current flows from the power supply, through the brushes and commutator, and into the coil, the two vertical sides of the coil (within the magnetic field of the permanent magnets) experience forces due to the motor effect.
2. Turning Effect (Torque): According to Fleming's Left-Hand Rule (or by observing the interaction of fields), the force on one side of the coil acts upwards, and the force on the other side acts downwards. These two forces are equal in magnitude and opposite in direction, but they are applied at different points on the coil, creating a turning effect (torque). This torque causes the coil to rotate.
3. Commutator's Role: As the coil rotates and reaches a vertical position (where the forces would act to stop the rotation), the brushes momentarily lose contact with one commutator segment and make contact with the next. This causes the direction of the current in the coil to reverse.
4. Continuous Rotation: Because the current direction reverses at just the right moment, the direction of the forces on the coil sides also reverses. This ensures that the forces continue to create a turning effect in the same rotational direction, allowing the coil to spin continuously. The inertia of the coil carries it through the brief moment of current reversal.
5. Conversion: Electrical energy supplied by the battery is continuously converted into the kinetic energy of the rotating coil, and subsequently, into useful mechanical work.

The strength of the turning effect (torque) produced by a DC motor, and thus its ability to do work, can be increased by:
- Increasing the current: A larger current in the coil creates a stronger magnetic field from the coil, leading to a stronger interaction with the external field.
- Increasing the strength of the external magnetic field: Using stronger permanent magnets or more powerful electromagnets for the stator.
- Increasing the number of turns in the coil: More turns mean more current-carrying segments experiencing the force, resulting in a greater total turning effect.
- Increasing the area of the coil: A larger coil area means the forces on the sides are exerted further from the axis of rotation, increasing the turning effect.
- Inserting a soft iron core inside the coil: The soft iron core becomes a temporary magnet when current flows, significantly concentrating and strengthening the magnetic field of the coil itself, which then interacts more strongly with the external field.