Final answer:
The direction of a magnetic field at a location is indicated by the direction the north pole of a small compass needle points, which is towards the south pole of the magnet it is detecting.
Step-by-step explanation:
The direction of a magnetic field at any point is indicated by the direction that the north pole of a small compass needle points when placed at that location. Therefore, the correct answer to how a magnetic field direction is indicated is: b) A magnetic field is always directed in the direction that the north pole of a small compass needle points at the location.
In practice, tiny compasses are used to map the magnetic field around a magnet. They align themselves in the direction of the magnetic field lines, which flow from the north pole of the magnet to its south pole. This means that outside the magnet, the magnetic field lines are directed towards the south pole and away from the north pole. Internally, they form continuous closed loops that complete the magnetic circuit.
It's important to remember that the Earth's north magnetic pole actually functions as a south pole in terms of a bar magnet's definition. Thus, a compass needle's north pole is attracted toward the Earth's north magnetic pole, which is geographically in the Arctic.