Worked example: A rectangular coil (10 cm × 6 cm, 50 turns) carries 3 A in a 0.5 T field. (a) Maximum torque? (b) Torque when the normal makes 30° with B? (c) What does the commutator do? Step 1: A = 0.1 × 0.06 = 0.006 m². τmax = NBIA = 50 × 0.5 × 0.006 × 3 = 0.45 N·m. Step 2: τ = τmax·sinθ = 0.45 × sin30° = 0.225 N·m. Step 3: As the coil rotates past θ = 0 (torque zero, but inertia carries it through), the split-ring commutator swaps the brush contacts, reversing I — so τ keeps pushing the same way instead of pulling back. Without it, the coil would just oscillate around alignment like a compass needle; with it, you get a motor.