The needle is measuring the air temperature. The needle is showing the direction of the wind. The needle is lining up with Earth's magnetic poles. The needle is pointing to the magnetic core of Earth.
I gave my students this multiple choice question: A compass can be made by magnetizing a needle and setting it on a floating cork. The cork will turn so that the needle is pointed north. Which statement explains why the needle points north?

Only one answer is correct among these 4 choices:
- The needle is measuring the air temperature.
- The needle is showing the direction of the wind.
- The needle is lining up with Earth's magnetic poles.
- The needle is pointing to the magnetic core of Earth.

Could you tell me which one is correct?

The needle is lining up with Earth's magnetic poles.