题目内容

To maintain the current airway systems, a great number of VOR ground stations are needed.

A. 对
B. 错

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Fill in each blank with NO MORE THAN THREE words from the text.To use aircraft as a ________, a navigation system is a must need. Today's most popuplar air navigation system is the Very High Frequency , or VOR. First developed in the US, it is a _radio navigation system consisting of many fixed and a receiver unit on board. The _it uses ranges from 108 to 117.95 MHz, and its maximum range is 200nm ________ and 25nm in the terminal area.

当用白光照射光栅时（）

A. 中央明纹为白色
B. 中央明纹为彩色
C. 同一级明纹中，红光在内，紫光在外
D. 只会产生衍射

在单缝夫琅禾费衍射中，对于给定的单色光，将单缝沿着透镜光轴方向向透镜平移，则屏幕上的衍射条纹（填变密或变疏或不变）；当缝宽变小时，除中央亮纹的中心位置不变以外，各级衍射条纹对应的衍射角。（填变大或变小）

假设透射光栅的总缝数为N，则在两个主极大之间有个暗纹和个次极大。