The correct option is Bar magnet.
Explanation
A magnetic compass utilizes a magnetized needle that is free to rotate in a horizontal plane. The fundamental physical property governing its operation is the interaction between a permanent magnet and an external magnetic field.Detailed Analysis:
- Bar magnet is Correct: A magnetic compass needle is essentially a small, lightweight bar magnet pivoted at its center. Like a standard bar magnet, it possesses a North pole and a South pole. When placed in a magnetic field (such as the Earth's magnetic field), it experiences a torque that aligns its magnetic axis parallel to the magnetic field lines.
- Solenoid is Incorrect: A solenoid is a cylindrical coil of wire that acts as a magnet only when an electric current flows through it (electromagnet). A standard compass needle is a permanent magnet and does not rely on electric current.
- Galvanometer is Incorrect: A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. While it utilizes magnetic principles, a compass needle itself is not a galvanometer.
- Resistor is Incorrect: A resistor is a passive electrical component that creates resistance in the flow of electric current. It does not possess the magnetic properties required for a compass.
Key Takeaway:
A magnetic compass needle functions as a tiny bar magnet, aligning itself with the Earth's magnetic North-South direction due to the torque exerted by the Earth's magnetic field.