Quick questions on Magnetic force on a current and the DC motor: VCE Physics Unit 3

A straight wire of length $L$ carrying current $I$, with $n$ turns or wires, in a uniform field $B$ perpendicular to the current, feels a force:

Consider a rectangular coil of $n$ turns, width $w$ and length $L$, carrying current $I$ in a uniform field $B$ parallel to the plane of the coil. The forces on the two long sides are equal in magnitude ($F = n B I L$) but opposite in direction (one up, one down). These forces form a couple that rotates the coil about its axis.

A simple DC motor consists of:

A real motor has hundreds of turns ($n$ large) to multiply the torque without needing huge currents. A laminated iron core inside the coil concentrates the field $B$, increasing torque further. Multiple coils at different angles smooth out the torque so the rotation is uniform rather than pulsing.

VCE coils have many turns; missing $n$ gives an answer too small by a factor of 50 or 100.

A split-ring commutator reverses the current direction in the coil every half-turn (used in DC motors and DC generators). Slip rings keep the connection continuous (used in AC generators).

The torque is momentarily zero at the vertical position, but the coil's inertia carries it past, and after the commutator swaps the contacts the torque resumes in the same rotational direction.

Conventional current flows from + to -, opposite to the electron drift. Apply the right-hand rule using conventional current.