Physics - Electromagnetism (Magnetic fields and Motors)

Magnetic field lines originate from the North ($N$) pole and terminate at the South ($S$) pole. The density of lines indicates the strength of the field ($B$).

The magnetic field around a straight current-carrying wire forms concentric circles. Its direction is determined by the Right-Hand Grip Rule: Thumb points to current ($I$), fingers curl in the direction of the field ($B$).

A solenoid is a long coil of wire. The field inside is strong and uniform. Strength can be increased by increasing the current ($I$), increasing the number of turns ($N$), or adding a soft iron core.

The Motor Effect: When a current-carrying conductor is placed in an external magnetic field, it experiences a force ($F$) due to the interaction of the fields.

Fleming's Left-Hand Rule determines the direction of the force: Thumb = Force/Motion ($F$), First Finger = Magnetic Field ($B$ from $N$ to $S$), Second Finger = Current ($I$ from $+$ to $-$).

In a DC Motor, a split-ring commutator reverses the direction of the current every half-turn to ensure the coil continues to rotate in the same direction.

The magnitude of the force on a wire is proportional to the magnetic flux density ($B$), the current ($I$), and the length of the wire ($L$) within the field.