Physical Experiment Report "Photometric Wavelengths Using Spectrometers and Transmission Gratings"
【Purpose】
Observe the diffraction spectrum of the grating, and master the method of measuring the wavelength of the light by the spectrometer and the transmission grating.
【laboratory apparatus】
Spectrometer, transmission grating, sodium light, incandescent lamp.
[Experimental principle]
A grating is a very good beam splitting element that separates light of different wavelengths and forms bright, narrow lines.
There are two types of gratings: transmission grating and reflection grating. In this experiment, a transmission grating is used. It is engraved on a transparent screen with a large number of elements that are parallel to each other and equally spaced, and the notch is opaque. The light is transmitted, so that a large number of equally wide and equally spaced slits are formed on the screen. The sum of the width of the score and the slit is called the grating constant and is denoted by d.
According to the theory of grating diffraction, when a parallel beam of light is perpendicularly projected onto the plane of the grating, the light passing through each slit will be single-slit diffraction, and the light passing through all the slits will interfere with each other. The grating diffraction spectrum The strength is determined by both the single slit diffraction and the interstitial interference. A converging lens can be used to converge the diffraction spectrum of the grating onto the focal plane of the lens. Where the diffraction angle satisfies the following conditions
k = 0, ±1, ±2, ...
The diffracted light will be strengthened in the direction of the diffraction angle to produce bright streaks, and the light in other directions will cancel in whole or in part. This is called the grating equation. Where d is the grating constant of the grating, θ is the diffraction angle, and λ is the wavelength of the light wave. When k=0, θ=0 gives zero-order bright lines. When k = ±1, ±2 ..., the symmetry is separated on the two sides of the zero-order stripe, the second level...
In the experiment, if the diffraction angle θ of the k-th plain line is measured and the grating constant d is known, the wavelength λ of the light wave to be measured can be calculated by the grating equation.
[Experimental content and steps]
1. Spectrometer adjustment
The adjustment method of the spectrometer is shown in Experiment 1.
2. Wavelength of light diffraction by grating diffraction
To measure the wavelength of a light wave using a grating equation, it is necessary to adjust the grating plane perpendicular to the optical axis of the collimator and the telescope. The sodium light is used to illuminate the slit of the collimator, so that the center perpendicular of the reticle in the telescope eyepiece is aligned with the image of the slit, and then the telescope is fixed. Place the grating bracket with the grating on the stage, align one end with the leveling screw a and one end at the midpoint of the other two leveling screws b, c. As shown in Figure 12, rotate the vernier disk. And adjust the leveling screw b or c. When the "Ten" word reflected from the grating plane coincides with the cross line above the reticle, as shown in FIG. 13, the vernier disk is fixed.
Figure 12 Location of the grating bracket Figure 13 Reticle
Adjust the grating notch parallel to the axis of rotation. Illuminate the slit with sodium light, loosen the telescope fastening screw, turn the telescope to observe the ±1, ±2 diffraction spectrum on both sides of the 0-level spectrum, and adjust the leveling screw a to make the midpoint of the spectral lines on both sides It coincides with the center of the center crosshair of the reticle, even if the spectral lines on both sides are equal. Repeat the adjustment until both conditions are met.
Measuring the wavelength of sodium yellow light
1 Rotate the telescope to find the zero-order image and coincide with the center perpendicular on the reticle. Read the two angles θ0 and θ0/ in the radial direction on the dial and record them in Table 4.
2 Turn right to the telescope, find the first-level image, and make it coincide with the center vertical line on the reticle. Read the two angles θ right and θ right/ on the dial in the radial direction and record them in Table 4.
3 Turn left to the telescope, find the first-level image on the other side, and make it coincide with the center perpendicular on the reticle. Read the two angles θ left and θ left/ on the dial in the radial direction and record them in Table 4. in.
3. Observe the diffraction spectrum of the grating.
The light source is replaced by a composite light source to observe the diffraction spectrum of the grating through a telescope.
【Precautions】
1. The adjustment of the spectrometer is very time consuming. After the adjustment, do not change the experiment arbitrarily, so as to avoid re-adjustment and affect the experiment.
2. The grating used in the experiment is a replica grating made of gelatin. The gelatin on the glass plate of the diffraction grating should not be touched by hand or rubbed with paper to avoid damage to the surface.
3. Before turning the telescope, loosen the screw that fixes it; when turning the telescope, the hand should hold the bracket and rotate it.
[data recording and processing]
Table 4 diffraction angle of the first-order line
Zero-order image position
Left pass image position
Deflection angle
Turn right to the first level image position
Deflection angle
Deflection angle average
Grating constant
The wavelength of sodium light λ0 = 589·3 nm
According to the formula K=1, λ= d sin 1=
Relative error
[thinking questions]
1. What is the minimum deflection angle? How to find the minimum deflection angle?
2. What are the four main components of the spectrometer? What is the role of each?
3. What is important to adjust the optical axis of the telescope perpendicular to the central axis of the spectrometer? How can I ensure that the green crosshair image reflected by the double-sided mirror is visible in the telescope?
4. Why use the grating photometric wavelength to make the optical axis of the collimator and telescope perpendicular to the grating plane?
5. What phenomenon was observed when experimenting with a composite light source, how to explain this phenomenon?
Observe the diffraction spectrum of the grating, and master the method of measuring the wavelength of the light by the spectrometer and the transmission grating.
【laboratory apparatus】
Spectrometer, transmission grating, sodium light, incandescent lamp.
[Experimental principle]
A grating is a very good beam splitting element that separates light of different wavelengths and forms bright, narrow lines.
There are two types of gratings: transmission grating and reflection grating. In this experiment, a transmission grating is used. It is engraved on a transparent screen with a large number of elements that are parallel to each other and equally spaced, and the notch is opaque. The light is transmitted, so that a large number of equally wide and equally spaced slits are formed on the screen. The sum of the width of the score and the slit is called the grating constant and is denoted by d.
According to the theory of grating diffraction, when a parallel beam of light is perpendicularly projected onto the plane of the grating, the light passing through each slit will be single-slit diffraction, and the light passing through all the slits will interfere with each other. The grating diffraction spectrum The strength is determined by both the single slit diffraction and the interstitial interference. A converging lens can be used to converge the diffraction spectrum of the grating onto the focal plane of the lens. Where the diffraction angle satisfies the following conditions
k = 0, ±1, ±2, ...
The diffracted light will be strengthened in the direction of the diffraction angle to produce bright streaks, and the light in other directions will cancel in whole or in part. This is called the grating equation. Where d is the grating constant of the grating, θ is the diffraction angle, and λ is the wavelength of the light wave. When k=0, θ=0 gives zero-order bright lines. When k = ±1, ±2 ..., the symmetry is separated on the two sides of the zero-order stripe, the second level...
In the experiment, if the diffraction angle θ of the k-th plain line is measured and the grating constant d is known, the wavelength λ of the light wave to be measured can be calculated by the grating equation.
[Experimental content and steps]
1. Spectrometer adjustment
The adjustment method of the spectrometer is shown in Experiment 1.
2. Wavelength of light diffraction by grating diffraction
To measure the wavelength of a light wave using a grating equation, it is necessary to adjust the grating plane perpendicular to the optical axis of the collimator and the telescope. The sodium light is used to illuminate the slit of the collimator, so that the center perpendicular of the reticle in the telescope eyepiece is aligned with the image of the slit, and then the telescope is fixed. Place the grating bracket with the grating on the stage, align one end with the leveling screw a and one end at the midpoint of the other two leveling screws b, c. As shown in Figure 12, rotate the vernier disk. And adjust the leveling screw b or c. When the "Ten" word reflected from the grating plane coincides with the cross line above the reticle, as shown in FIG. 13, the vernier disk is fixed.
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Figure 12 Location of the grating bracket Figure 13 Reticle
Adjust the grating notch parallel to the axis of rotation. Illuminate the slit with sodium light, loosen the telescope fastening screw, turn the telescope to observe the ±1, ±2 diffraction spectrum on both sides of the 0-level spectrum, and adjust the leveling screw a to make the midpoint of the spectral lines on both sides It coincides with the center of the center crosshair of the reticle, even if the spectral lines on both sides are equal. Repeat the adjustment until both conditions are met.
Measuring the wavelength of sodium yellow light
1 Rotate the telescope to find the zero-order image and coincide with the center perpendicular on the reticle. Read the two angles θ0 and θ0/ in the radial direction on the dial and record them in Table 4.
2 Turn right to the telescope, find the first-level image, and make it coincide with the center vertical line on the reticle. Read the two angles θ right and θ right/ on the dial in the radial direction and record them in Table 4.
3 Turn left to the telescope, find the first-level image on the other side, and make it coincide with the center perpendicular on the reticle. Read the two angles θ left and θ left/ on the dial in the radial direction and record them in Table 4. in.
3. Observe the diffraction spectrum of the grating.
The light source is replaced by a composite light source to observe the diffraction spectrum of the grating through a telescope.
【Precautions】
1. The adjustment of the spectrometer is very time consuming. After the adjustment, do not change the experiment arbitrarily, so as to avoid re-adjustment and affect the experiment.
2. The grating used in the experiment is a replica grating made of gelatin. The gelatin on the glass plate of the diffraction grating should not be touched by hand or rubbed with paper to avoid damage to the surface.
3. Before turning the telescope, loosen the screw that fixes it; when turning the telescope, the hand should hold the bracket and rotate it.
[data recording and processing]
Table 4 diffraction angle of the first-order line
Zero-order image position
Left pass image position
Deflection angle
Turn right to the first level image position
Deflection angle
Deflection angle average
Grating constant
The wavelength of sodium light λ0 = 589·3 nm
According to the formula K=1, λ= d sin 1=
Relative error
[thinking questions]
1. What is the minimum deflection angle? How to find the minimum deflection angle?
2. What are the four main components of the spectrometer? What is the role of each?
3. What is important to adjust the optical axis of the telescope perpendicular to the central axis of the spectrometer? How can I ensure that the green crosshair image reflected by the double-sided mirror is visible in the telescope?
4. Why use the grating photometric wavelength to make the optical axis of the collimator and telescope perpendicular to the grating plane?
5. What phenomenon was observed when experimenting with a composite light source, how to explain this phenomenon?
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