Question

which will produce a magnetic field?
○ any wire with or without a current
○ a wire formed into a coil
○ a wire carrying a current
○ a wire formed into a single loop

Explanation:

To determine which produces a magnetic field, we recall the principle of electromagnetism: a magnetic field is generated by moving electric charges, i.e., an electric current.

• "Any wire with or without a current": A wire without current has no moving charges, so no magnetic field. Eliminate this.
• "A wire formed into a coil": A coil without current (just the shape) doesn’t produce a magnetic field. The shape alone isn’t enough—current is needed. Eliminate this.
• "A wire carrying a current": Moving charges (current) in the wire create a magnetic field (Oersted’s discovery). This fits.
• "A wire formed into a single loop": A single loop without current (just the looped shape) doesn’t produce a magnetic field. Current is required. Eliminate this.

Answer:

C. a wire carrying a current (Note: Assuming the options are labeled A, B, C, D with A as "any wire...", B as "a wire formed...coil", C as "a wire carrying...", D as "a wire formed...loop")