Final answer:
The query involves calculating the current needed in a power line to create a magnetic field that could disrupt compass readings, illustrating the application of electromagnetism in real-life situations.
Step-by-step explanation:
The question relates to the magnetic field created by an electric current in a long straight wire and its potential to interfere with compass readings. To determine the current needed to create a specific magnetic field at a given distance, we use the formula derived from Ampère's law. While the useable distance of a compass is not explicitly answered, we can infer that fields comparable to Earth's typical magnetic field strength (around 5.00×10-5 T) could cause interference. For example, assuming a surveyor is 100 meters away from a 200-kV DC power line, if the wire is not paired with another to cancel out the magnetic field, the resulting field could be about 10 times stronger than Earth's field, significantly affecting a compass's use within that proximity.
In an effort to calculate the unreasonable result mentioned, the given example indicates that a surveyor suspects the magnetic field from a power line may be disrupting compass readings. An analytical approach is needed to solve for the current using the magnetic field strength and distance from the wire. The premise that a surveyor needs to deal with such interference underlines the practical relevance of electromagnetism in everyday situations like surveying.