Atomic Spectra

Interference and diffraction are traveling wave phenomena. When light is forced to go through a narrow slit or pinhole or when it passes a sharp-edged obstruction, it shows its wave nature. For example, when the shadow of a razor blade is examined under high magnification it is found to be a series of closely-spaced bright and dark bands. The series of bands is called a diffraction pattern. Diffraction and interference in waves are the result of reinforcement or cancelation of waves when different waves are at the same point in space at the same time. If the diffraction pattern of the razor's edge is viewed in blue light and then in red light, it is found that the bright and dark bands are closer together in the blue light because its wavelength is shorter. This is one way to confirm the basic theories about the wave nature of light.

干涉和衍射是波动现象。当光被强制通过一个狭缝或针孔，或者在遇到一个尖锐边缘的障碍物时，它会表现出波动性。例如，当用高倍放大镜观察剃刀刀刃的影子时，会发现是一系列紧密排列的明暗条纹。这些条纹被称为衍射图样。波的干涉和衍射是由于在空间中同一位置同时存在不同波时，波的加强或抵消所导致的。如果用蓝光和红光分别观察剃刀边缘的衍射图样，会发现蓝光下的明暗条纹更紧密，因为蓝光的波长更短。这是确认光波动性的基本理论的一种方法。

Diffraction through a series of closely spaced slits (called a grating) serves a useful purpose for the examination of the different wavelengths of light. Diffraction of a narrow beam of light of a single wavelength by a grating will produce a bright beam straight ahead and a series of beams to either side at angles where the light waves from adjacent slits reinforce each other. The first bright image to either side occurs when the difference in the pathlength of the light from adjacent slits of the grating is one wavelength, and it is called the "first order" diffraction maximum. When the pathlength difference is two wavelengths, another bright image occurs (the second order diffraction maximum). If light of a longer wavelength is used, the maxima are at larger angles. When light of multiple wavelengths is used, the different wavelengths(different colors) are separated. The separation of the colors is much larger than that obtained with a prism, so a diffraction grating can be thought of as a "super prism".

通过一系列紧密排列的狭缝（称为光栅）发生的衍射在研究不同波长的光方面具有实用价值。当一束单色光通过光栅发生衍射时，会在正前方产生一束明亮的光，并在两侧产生一系列光束，这些光束在特定角度处形成，该角度使得相邻狭缝的光波相互加强。两侧的第一个明亮图像出现在光栅相邻狭缝的光程差为一个波长时，称为“第一级衍射极大值”。当光程差为两个波长时，另一个明亮图像出现（称为“第二级衍射极大值”）。如果使用较长波长的光，极大值出现在更大的角度。当使用多种波长的光时，不同波长（不同颜色）会被分离。这种颜色的分离程度比使用棱镜时更大，因此可以将衍射光栅视为一种“超级棱镜”。

The gratings to be used in this experiment are transmission gratings which are made by ruling a large number of equally spaced parallel lines on a piece of glass, only a few wavelengths apart. The transparent positions between the lines act as narrow slits. The sketch below compares the spectra produced by a prism and a grating. The experiment involves a careful examination of the spectra (collection of separated wavelengths of light) for several light sources. In each case you are to examine the first order spectrun to the right of the zero angle. The relationship between the wavelength of the light and the angle of diffraction is

本实验中将使用的是透射光栅，它们是通过在一块玻璃上刻制大量等间距的平行线条制成的，这些线条之间的间距只有几个波长那么宽。线条之间的透明区域起到窄缝的作用。下图比较了棱镜和光栅产生的光谱。实验涉及对几种光源的光谱（即分离的波长的集合）进行仔细的观察。在每种情况下，你都需要观察零角度右侧的第一级光谱。光的波长与衍射角之间的关系是

where n is the order number, θ is the angle of diffraction, and d is the distance between grating lines. For these gratings, there are 600 lines/mm which corresponds to a grating spacing of d = 1670 nanometers. The sine of the angles you measure ( sinθ )

其中，n 是级数，θ 是衍射角，d 是光栅线间距。对于这些光栅，每毫米有 600 线，对应光栅间距 d = 1670 纳米。你测量的角的正弦值（sinθ）

1. Place the diffraction grating in the mount at the center of the round metal diffractometer table and align it perpendicular to the path of the light.

将衍射光栅放在圆金属衍射仪台面的中心，并使其垂直于光的路径。

2. Place the helium spectral tube in the holder and adjust its position for maximum intensity when viewed through the slit from the front.

将氦气谱管放入支架中，并调整其位置，使其从正面通过狭缝观察时具有最大强度。

a. View the slit through the telescope. Note the angle reading when the cross hairs are on the slit. If it is not zero, consult the lab supervisor.

通过望远镜观察狭缝。当十字线对准狭缝时，记录角度读数。如果读数不为零，请咨询实验室负责人。

b. Locate the first order green line to the right. It should be at about the 18° position. Record its angle.

找到右侧的第一级绿色谱线，它应位于约18°的位置。记录其角度。

c. Locate the same first order line to the left. Record its angle from zero (that is, 360° - θ_left).

c. 将左侧的同一一级光谱线定位到左侧。记录其从零点的角度（即360° - θ_left）。

d. Find the average of the results of parts b. and c. Place the telescope at the average angle to the right.

d. 计算b部分和c部分结果的平均值。将望远镜放置在平均角度的右侧。

e. Carefully rotate the grating until the same green line is at the crosshair. This places the grating perpendicular to the light beam. DO NOT MOVE THE GRATING FOR THE REMAINDER OF THE LAB.

e. 谨慎地旋转光栅，直到绿色谱线对准十字线。这使光栅垂直于光束。在实验的其余部分中，不要移动光栅。

3. View the first order (right) spectrum of helium and record the angle of each bright line with a line on one of the angle graphs provided. Indicate the color of the line.

观察氦气的第一级光谱（右侧）并用其中一个角度图上的直线记录每条明亮线的角度。标明每条线的颜色。

4. Repeat (3.) with the hydrogen(H) and mercury (Hg) tubes. Observe the neon(Ne) tube, but you are not required to plot those lines.

4. 重复步骤(3)，使用氢气(H)和水银(Hg)管。观察氖气(Ne)管，但不需要绘制这些谱线。

5. View the incandescent source. Recond on a graph the two angles of the extremes of the spectrum. Next, scan the spectrum and record the angles at which you find "pure" red, orange, yellow, green, blue, and violet. Use these measurements to indicate the corresponding color bands on your plot.

观察发光体。在图上记录光谱的两个极端角度。接下来，扫描光谱，并记录你找到的‘纯’红色、橙色、黄色、绿色、蓝色和紫色对应的角度。利用这些测量结果，在你的图上标出相应的颜色带。

1. Using the formula for wavelength, determine the wavelength for the two extremes found in part 5.

Atomic Spectra

Equipment: Atomic Spectra