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同一光源上同一个点在不同一时刻先后自发辐射发出的两列光波是:
A. 相干的
B. 不相干的
同一光源上不同部位两个点在同一时刻自发辐射发出的两列光波是:
A. 相干的
B. 不相干的
高斯白噪声是指噪声的概率密度服从______ 分布,功率谱密度服从______ 分布,通过带通滤波器后输出的信号包络服从______ 分布。
A system of N particles is free from any external forces. Which of the following is true for the magnitude of the total momentum of the system?
A. It must be zero.
B. It could be non-zero, but it must be constant.
C. It could be non-zero, and it might not be constant.
D. The answer depends on the nature of the internal forces in the system.