[填空题]
A micrometer is conn7*cz/48.e- yifinwn; w wieihected to kscog30a15b zr8xee-jn 0t+otsf /2gthe movable mirror of an interferometer. When the micrometer is tightened down on a thin metal foil, the net number of bright fringes that move, compared to the empty micrometer, is 272. What is the thickness of the foil? The wavele5-t z1 0c3ek/et gn+xf2brs0o 8ja ogsngth of light used is 589 nm. $\mu m$
