field strength measured in Oersted
s (Oe) required to 'flip' the polarity
of a bar magnet with two stable
e.g. place a magnetic particle in a strong magnetic field of the opposite polarity and the particle's polarity will swap (north to south, south to north).
Credit cards and other cards with magnetic strips/stripes are made in a high-engery and a low-energy form. High-energy cards take ~4,000 Oersteds to encode. Low-energy cards require a mere ~300 Oersteds.