[填空题]
A total of 31 bright and 31 dark Newton’s ringsd*5 ,tps6eq cw (not counb+uk5i7 r0w6pny z+n3sef6 ijting the dark spot at t jwrf bzs30 y+6+ k6upn5eii7nhe center) are observed when 550-nm light falls normally on a planoconvex lens resting on a flat glass surface (Fig. 24–31). How much thicker is the center than the edges? $\mu m$
