When using magnets, How does a compass determine the quantitative value of the magnitude and the direction of the magnetic field?
Asked
Active
Viewed 366 times
2 Answers
2
One wouldn't use this method outside an undergraduate laboratory, but it is possible to use a compass to determine the strength of the horizontal component of a magnetic field... Displace the compass magnet by a small angle (say < 10°) from its equilibrium position, that is aligned with the local magnetic field. The needle will return towards its equilibrium position in a series of damped oscillations. Provided the damping is quite light (and, unfortunately, most modern compasses are liquid-filled, so too heavily damped), the period of oscillation is $$T=2\pi \sqrt{\frac I{mB}}$$ in which $I$ is the moment of inertia of the magnet/needle assembly and $m$ is the magnet's magnetic moment. [The constant $I/m$ is found by measuring the period of oscillation in a known magnetic field.]
Philip Wood
- 37,325
0
The earth has the North Pole and the South Pole, they have magnetic fields which flow from North to South. A compass needle tracks onto these magnetic fields, and therefore pointing Noth (the Geographical North Pole is actually South facing).
