DC Motor Speed Factors Steps:

• Torque in a DC motor is given by τ = N B I A sinθ, where N is turns, B is field strength, and I is current; higher torque can increase speed against load.
• Back EMF E = k N B ω, where ω is angular speed; speed adjusts to balance E with applied voltage minus IR drop.
• Increasing B strengthens flux, altering ω inversely but still affecting speed.
• Changing N or I modifies k or voltage drop, directly impacting equilibrium speed.

Why A is correct:

• The DC motor speed formula n ≈ (V - I R)/(k φ) shows speed depends on B (via flux φ), N (via constant k), and I (via IR drop), confirming all three factors influence rotation speed.

Why the others are wrong:

• B omits current, but I affects speed through armature resistance drop.
• C omits turns, but N scales the motor constant, altering speed.
• D omits field, but B determines flux, inversely affecting speed.

Final answer: A