What causes deviation in a magnetic compass?

The correct answer pertains to the influence of external magnetic fields on a magnetic compass. A magnetic compass is designed to align itself with Earth's magnetic field to provide direction; however, when there are additional magnetic fields present in the vicinity, such as those generated by electrical circuits, machinery, or even nearby vehicles, these can interfere with the compass's ability to accurately indicate the true magnetic direction.

When external magnetic fields exert their influence, they can cause the magnetic compass to give false readings, leading to navigational errors. This interference is particularly critical for pilots and mariners, who rely on compass readings for safe navigation. Thus, understanding the impact of external magnetic fields is crucial for potential errors in directional navigation.

Magnetic declination, on the other hand, is a geographic phenomenon related to the difference between true north and magnetic north and does not directly cause fluctuations in compass readings due to interference. Instrument malfunction could also cause inaccuracies, but it would not be classified under the broader influence of external magnetic fields. Therefore, recognizing the role of external magnetic fields helps address potential compass deviations effectively.