Assertion (A): A magnetic compass is the standard tool used to "see" the invisible magnetic field around a bar magnet. By placing the compass at various points and marking the direction the needle points, you can connect the dots to trace continuous magnetic field lines.Reason (R): The compass needle is itself a tiny bar magnet. According to the fundamental law of magnetism—opposite poles attract—the north pole of the compass needle will always be attracted to and point toward the south pole of the bar magnet (and away from its north pole).The reason we can trace field lines with a compass is precisely because the needle responds to the magnetic force by aligning itself with the field at that specific point.By definition, magnetic field lines outside a magnet emerge from the North pole and enter the South pole.Because the compass's north pole is always "pulled" toward the magnet's south pole, the needle acts as a directional pointer that allows us to map the entire path of the field.