[填空题]
A total of 31 bright and 31 dark Newton’s ri)wjqly08s jc*19n 9( esr5k pjwb o6gangs (not counting the d/mqv+qlti l) 4ark spot at the center) are observtqllm4 +q vi/)ed 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? $\mu m$
