The needle shows a deflection.
Explanation
The phenomenon in Oersted’s Experiment (1820), which established the relationship between electricity and magnetism. It demonstrated that an electric current flowing through a conductor generates a magnetic field around it.
Detailed Analysis:
- The needle rotates continuously. is Incorrect: A wire carrying direct current (DC) produces a steady, non-fluctuating magnetic field. The compass needle will align with this field and stop; it will not rotate continuously. Continuous rotation would require a changing magnetic field or a specific motor mechanism (like a commutator).
- The needle shows a deflection. is Correct: When current flows through the wire, it creates a magnetic field in the surrounding space (concentric circles around the wire). The magnetic needle of the compass experiences a magnetic torque due to this field and deflects from its original North-South alignment to align with the resultant magnetic field vector.
- The needle becomes demagnetized. is Incorrect: Demagnetization of a permanent magnet (like a compass needle) typically requires heating above the Curie temperature or exposure to a strong, alternating magnetic field. A static magnetic field from a DC wire does not demagnetize the needle.
- The needle is electrostatically repelled. is Incorrect: The interaction between the current-carrying wire and the compass is magnetic, not electrostatic. While charges flow in the wire, the net wire is electrically neutral, and the compass needle responds to magnetic poles, not electric charge.
Key Takeaway:
A current-carrying conductor produces a magnetic field around it, which exerts a magnetic force on other magnets, such as a compass needle, causing deflection.