Motor speed depends on current from voltage

Steps:

• Motor coil rotation frequency is proportional to torque on the coil.
• Torque τ = N B I A (simplified for max effect), where I is current.
• Current I = V / R by Ohm's law, so frequency scales with voltage V.
• Lower voltage reduces I, torque, and rotation frequency.

Why C is correct:

• Lower voltage decreases current (I = V/R), reducing torque and rotation frequency per motor principles.

Why the others are wrong:

• A: More turns increases torque (higher N in τ = N B I A), raising frequency.
• B: Reversing current changes rotation direction but not frequency.
• D: Stronger magnet increases torque (higher B in formula), raising frequency.

Final answer: C