Physics
Physics
Problem
Two identical bar magnets are placed on a table with their north poles facing each other and 4 cm apart. Point P lies exactly midway between the two north poles. What is the net magnetic field at point P? a) From left to right, toward the right-hand magnet b) Vertically upward, out of the plane of the table c) Zero, because the two fields are equal and opposite d) From right to left, toward the left-hand magnetIntuitive explanation
The key insight is that magnetic field is a vector—it has both magnitude and direction. Each magnet creates a field pointing away from its north pole, so at the midpoint P, both fields point in opposite directions along the line connecting the magnets. Since the magnets are identical and equidistant from P, the field strengths are equal, meaning the vectors cancel completely. This is a beautiful example of how symmetry can eliminate a quantity entirely.
Intuitive explanation
The key insight is that magnetic field is a vector—it has both magnitude and direction. Each magnet creates a field pointing away from its north pole, so at the midpoint P, both fields point in opposite directions along the line connecting the magnets. Since the magnets are identical and equidistant from P, the field strengths are equal, meaning the vectors cancel completely. This is a beautiful example of how symmetry can eliminate a quantity entirely.