A navigator at 40∘ N latitude measures that her compass points 10∘ west of geographic north. Which of the following best accounts for this westward declination?
a) Local iron-ore deposits beneath the region distort Earth’s field, causing the compass to deviate 10∘ west of true north.
b) Because Earth’s magnetic dipole axis is tilted relative to its rotation axis, the magnetic pole lies west of geographic north at that longitude, giving a 10∘ westward declination.
c) As Earth rotates, the Coriolis force acts on the compass needle and deflects the north-seeking end toward the west.
d) Electric currents in the ionosphere induced by solar radiation create a secondary magnetic field that opposes Earth’s field locally, swinging the needle 10∘ westward.