Which pair correctly describes two observable effects of Earth’s magnetic field?

• A. It sets Earth’s surface gravity and causes daily temperature variations.
• B. It generates the Coriolis force and creates Earth’s seasons.
• C. It causes compass needles to align roughly north–south and contributes to auroras by guiding charged particles toward the polar regions.
• D. It produces ocean tides and determines the phase of the Moon.

Answer: (C)

Verified step by step guidance

1. Identify the nature of Earth's magnetic field: it is a magnetic field generated by the motion of molten iron in Earth's outer core, which affects charged particles and magnetic materials.
2. Understand that Earth's magnetic field influences compass needles, causing them to align roughly along the north–south direction due to magnetic forces acting on the needle's magnetic dipole.
3. Recognize that charged particles from the solar wind are guided by Earth's magnetic field lines toward the polar regions, where they interact with the atmosphere to create auroras (Northern and Southern Lights).
4. Eliminate options that describe effects unrelated to the magnetic field, such as gravity, temperature variations, Coriolis force, seasons, ocean tides, and lunar phases, which are caused by other physical phenomena.
5. Conclude that the correct pair of observable effects of Earth's magnetic field are the alignment of compass needles and the contribution to auroras near the poles.