What is the cause of atmospheric pressure?
36. An air wedge is formed using two glass plates that are in contact along their left edge. When viewed by highly monochromatic light, there are exactly 4001 dark bands in the reﬂected light. The air is now evacuated (with the glass plates remaining rigidly ﬁxed) and the number of dark bands decreases to exactly 4000. The index of refraction of the air is: A. 0.00025 B. 0.00050 C. 1.00025 D. 1.00050 E. 1.00000, by deﬁnition ans: C 37. A glass (n =1 .6) lens is coated with a thin ﬁlm (n =1 .3) to reduce reﬂection of certain incident light. If λ is the wavelength of the light in the ﬁlm, the least ﬁlm thickness is: A. less than λ/4 B. λ/4 C. λ/2 D. λ E. more than λ ans: B 38. Two point sources, vi