Physical Experiment Report "Determination of Triangular Refractive Index"
【Purpose】
Measuring the refractive index of the glass prism by using a spectrometer;
【laboratory apparatus】
Spectrometer, glass prism, sodium light.
[Experimental principle]
The minimum deflection angle method is one of the basic methods for determining the refractive index of the triangular prism. As shown in FIG. 10, the triangle ABC represents the cross section of the glass prism, and AB and AC are optical surfaces that are transparent, also called the refractive surface, and the angle a is called The apex angle of the prism; BC is the frosted glass surface, called the bottom surface of the triangular prism. Assuming that a certain wavelength of light LD is incident on the AB surface of the prism and is emitted twice in the ER direction after refraction, the angle between the incident ray LD and the outgoing ray ER is called the deflection angle.
Figure 10 Refraction of the prism
From the geometric relationship in Figure 10, the deflection angle can be obtained.
Because the top angle a is satisfied, then
For a given prism, the angle a is fixed and varies with the sum. Which is related to , , and so on, so the function is actually a function, and the deflection angle changes only. It can be observed in the experiment that when changing, the deflection angle has a very small value, called the minimum deflection angle. In theory, it can be proved that at the time, there is a minimum. It is apparent that the direction of the incident light and the outgoing light at this time is symmetrical with respect to the triangular prism, as shown in FIG.
The article you are browsing is organized by the first 'Panwen.com', and the copyright belongs to the original author and the original source.
Figure 11 Minimum deflection angle
If it is used to indicate the minimum deflection angle, it will be substituted.
or
Because , because of , because
According to the law of refraction,
Formula and substituting:
It can be known from the formula that the refractive index n of the incident light of the triangular prism can be obtained by measuring the minimum deflection angle of the incident light and the apex angle of the triangular prism.
[Experimental content and steps]
1. Adjusting spectrometer
Adjust the spectrometer according to the requirements and steps in Experiment 24-1.
2. Adjusting the collimator
Remove the double-sided mirror and turn on the sodium light source.
Open the slit and loosen the slit lock screw 3. Observe from the telescope while moving the slit device 2 back and forth until the slit is clearly imaged. Then adjust the slit width to about 1 mm.
Adjust the inclination of the collimator. Turn the slit to the level and adjust the collimator optical axis elevation adjustment screw 29 so that the slit image coincides with the center line of the telescope reticle. Then turn the slit to the vertical direction so that it coincides with the vertical line of the reticle cross-tick line, without parallax. Finally, the slit device lock screw 3 is locked. At this time, the collimator emits parallel light, and the optical axis of the collimator coincides with the optical axis of the telescope. At this point, the spectrometer has been adjusted.
3. Measuring the refractive index of the prism
The prism is placed on the stage, and the normal of the refractive surface of the glass prism is at an angle of about 60 degrees to the axis of the collimator.
Observe the change in the deflection angle. The light source illuminates the slit, and the direction of the refracted light is judged according to the law of refraction. First observe the eye in this direction, you can see several parallel color lines, then slowly rotate the stage, pay attention to the movement of the line, observe the change of the deflection angle. Slowly turn the stage in a direction in which the deflection angle decreases, so that the deflection angle continues to decrease until the line is moved to a position and then moved in the opposite direction. This shows that there is a minimum value of the deflection angle. The deflection angle when the direction of movement of the line is reversed is the minimum deflection angle.
1 Observe the line with a telescope. When carefully rotating the stage, keep the telescope tracking the line and pay attention to the movement of a certain wavelength line. When the line is reversed, tighten the vernier disc brake screw 27 and adjust the vernier disc fine adjustment screw 26 to accurately find the position of the minimum deflection angle.
2 Measure the minimum deflection angle position. Rotate the telescope bracket 15 so that the line is at the center of the reticle, tighten the telescope bracket brake screw 21, and adjust the telescope fine adjustment screw 18 so that the central vertical line of the reticle cross-mark in the telescope is aligned with the center of the line. , read the angle sum of the refracted rays of the line from Cursor 1 and Cursor 2.
3 Determine the direction of the incident light. Remove the prism, loosen the telescopic brake screw 21, move the telescope bracket 15, align the telescope with the collimator, fine tune the telescope, and accurately position the slit image on the central vertical scale of the reticle, read separately from the two cursors. The angle of the incident light.
4 Press to calculate the minimum deflection angle.
5 Repeat steps 1~6 to measure the minimum deflection angle of each line in the mercury lamp spectrum.
6 Calculate the refractive index of the prism for each wavelength line according to the formula. Table 3 for calculating the refractive index n.
[data recording and processing]
Table 3 Measuring the minimum deflection angle
Sodium light wavelength number cursor 1 cursor 2
Measuring the refractive index of the glass prism by using a spectrometer;
【laboratory apparatus】
Spectrometer, glass prism, sodium light.
[Experimental principle]
The minimum deflection angle method is one of the basic methods for determining the refractive index of the triangular prism. As shown in FIG. 10, the triangle ABC represents the cross section of the glass prism, and AB and AC are optical surfaces that are transparent, also called the refractive surface, and the angle a is called The apex angle of the prism; BC is the frosted glass surface, called the bottom surface of the triangular prism. Assuming that a certain wavelength of light LD is incident on the AB surface of the prism and is emitted twice in the ER direction after refraction, the angle between the incident ray LD and the outgoing ray ER is called the deflection angle.
Figure 10 Refraction of the prism
From the geometric relationship in Figure 10, the deflection angle can be obtained.
Because the top angle a is satisfied, then
For a given prism, the angle a is fixed and varies with the sum. Which is related to , , and so on, so the function is actually a function, and the deflection angle changes only. It can be observed in the experiment that when changing, the deflection angle has a very small value, called the minimum deflection angle. In theory, it can be proved that at the time, there is a minimum. It is apparent that the direction of the incident light and the outgoing light at this time is symmetrical with respect to the triangular prism, as shown in FIG.
The article you are browsing is organized by the first 'Panwen.com', and the copyright belongs to the original author and the original source.
Figure 11 Minimum deflection angle
If it is used to indicate the minimum deflection angle, it will be substituted.
or
Because , because of , because
According to the law of refraction,
Formula and substituting:
It can be known from the formula that the refractive index n of the incident light of the triangular prism can be obtained by measuring the minimum deflection angle of the incident light and the apex angle of the triangular prism.
[Experimental content and steps]
1. Adjusting spectrometer
Adjust the spectrometer according to the requirements and steps in Experiment 24-1.
2. Adjusting the collimator
Remove the double-sided mirror and turn on the sodium light source.
Open the slit and loosen the slit lock screw 3. Observe from the telescope while moving the slit device 2 back and forth until the slit is clearly imaged. Then adjust the slit width to about 1 mm.
Adjust the inclination of the collimator. Turn the slit to the level and adjust the collimator optical axis elevation adjustment screw 29 so that the slit image coincides with the center line of the telescope reticle. Then turn the slit to the vertical direction so that it coincides with the vertical line of the reticle cross-tick line, without parallax. Finally, the slit device lock screw 3 is locked. At this time, the collimator emits parallel light, and the optical axis of the collimator coincides with the optical axis of the telescope. At this point, the spectrometer has been adjusted.
3. Measuring the refractive index of the prism
The prism is placed on the stage, and the normal of the refractive surface of the glass prism is at an angle of about 60 degrees to the axis of the collimator.
Observe the change in the deflection angle. The light source illuminates the slit, and the direction of the refracted light is judged according to the law of refraction. First observe the eye in this direction, you can see several parallel color lines, then slowly rotate the stage, pay attention to the movement of the line, observe the change of the deflection angle. Slowly turn the stage in a direction in which the deflection angle decreases, so that the deflection angle continues to decrease until the line is moved to a position and then moved in the opposite direction. This shows that there is a minimum value of the deflection angle. The deflection angle when the direction of movement of the line is reversed is the minimum deflection angle.
1 Observe the line with a telescope. When carefully rotating the stage, keep the telescope tracking the line and pay attention to the movement of a certain wavelength line. When the line is reversed, tighten the vernier disc brake screw 27 and adjust the vernier disc fine adjustment screw 26 to accurately find the position of the minimum deflection angle.
2 Measure the minimum deflection angle position. Rotate the telescope bracket 15 so that the line is at the center of the reticle, tighten the telescope bracket brake screw 21, and adjust the telescope fine adjustment screw 18 so that the central vertical line of the reticle cross-mark in the telescope is aligned with the center of the line. , read the angle sum of the refracted rays of the line from Cursor 1 and Cursor 2.
3 Determine the direction of the incident light. Remove the prism, loosen the telescopic brake screw 21, move the telescope bracket 15, align the telescope with the collimator, fine tune the telescope, and accurately position the slit image on the central vertical scale of the reticle, read separately from the two cursors. The angle of the incident light.
4 Press to calculate the minimum deflection angle.
5 Repeat steps 1~6 to measure the minimum deflection angle of each line in the mercury lamp spectrum.
6 Calculate the refractive index of the prism for each wavelength line according to the formula. Table 3 for calculating the refractive index n.
[data recording and processing]
Table 3 Measuring the minimum deflection angle
Sodium light wavelength number cursor 1 cursor 2
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- Physical Experiment Report "Determination of Triangular Refractive Index