They have a path difference of zero.

它们的路径差为零。

This is called the path difference.

这称为路径差异。

The same holds true for the path difference between the light from the center of the slit and the bottom.

这同样适用于来自狭缝中心的光与底部之间的光程差。

So light waves will interfere either constructively or destructively, depending on the size of this path difference.

因此，光波会产生建设性或破坏性干扰，具体取决于路径差异的大小。

As with the previous example, this also has to do with the path difference between individual rays passing through the single slit.

与前面的示例一样，这也与通过单个狭缝的各个光线之间的路径差异有关。

Say the light is angled so that the total path difference between the top and bottom of the slit is 1.5 wavelengths.

假设光是倾斜的，因此狭缝顶部和底部之间的总路径差为 1。5 个波长。

For a single slit, the path difference is between the light coming from the very top of the slit and the light coming from the very bottom of the slit.

对于单个狭缝，路径差是来自狭缝最顶部的光和来自狭缝最底部的光之间。

When the path difference between the top and bottom of the slit is equal to 1.5 wavelengths – or 2.5 wavelengths, and so on – there will be a bright line.

当狭缝顶部和底部之间的路径差等于 1。5 个波长或 2。5 个波长，以此类推时，就会出现一条亮线。

The path difference is equal to the width of the slit, D, times the sine of the angle between the point on the screen and a line straight from the slit to the screen.

路径差等于狭缝的宽度 D 乘以屏幕上的点与从狭缝到屏幕的直线之间的夹角的正弦值。

If the path difference is one wavelength long, then the path difference between the light from the top of the slit and the light from the center of the slit is only half a wavelength.

如果光程差是一个波长长，那么来自狭缝顶部的光与来自狭缝中心的光之间的光程差只有半个波长。

So a total path difference of a full wavelength means that for each light ray coming through the slit at that angle, there's a corresponding light ray that's shifted by half a wavelength.

因此，全波长的总路径差意味着对于以该角度穿过狭缝的每条光线，都有一条相应的光线偏移了半个波长。