Torque on a current-carrying coil in a magnetic field

Steps:

• Torque magnitude given by τ = N I A B sinθ, where N is turns, I is coil current, A is area, B is field strength, θ is angle.
• Increasing coil current I directly increases τ.
• Increasing electromagnet current strengthens B, increasing τ.
• Reversing coil current reverses torque direction but keeps magnitude unchanged.
• Increasing turns N directly increases τ.

Why C is correct:

• Reversing current reverses torque vector per right-hand rule but preserves magnitude, as τ depends on |I| in the formula.

Why the others are wrong:

• A: Directly increases I, proportional to τ.
• B: Increases B via electromagnet, proportional to τ.
• D: Directly increases N, proportional to τ.

Final answer: C