to produce a heat source to demonstrate frictional forces to create a magnetic field to generate a sound wave
I gave my students this multiple choice question: Wire was looped several times around an iron nail, and the wire's ends were connected to a battery. For which of these will this device most likely be used?

Only one answer is correct among these 4 choices:
- to produce a heat source
- to demonstrate frictional forces
- to create a magnetic field
- to generate a sound wave

Could you tell me which one is correct?

to create a magnetic field