如图,在双缝干涉实验中,若把一厚度为e、折射率为n的薄云母片覆盖在S1缝上,中央明条纹将向___移动;覆盖云母片后,两束相干光至原中央明纹O处的光程差为___。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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