As the most commonly used instrument in biological experiments, whether a microscope can be used correctly is directly related to the success or failure of many biological experiments. Pointing out some errors in the use of microscopes by students and guiding students to use microscopes correctly should be an extremely important part of biological experiment teaching in middle schools. In the practice of biology teaching, the author observes that the students use the microscope operation process, and some problems reflected in the students' experimental examination, I think the following points teachers need to emphasize in the lecture.
First, the problem of correct installation
Before using the microscope, first install the microscope eyepiece and objective lens. The installation of the eyepiece is relatively simple, the main problem is the installation of the objective lens, because the objective lens is more expensive, in case the screw thread is not properly closed during the installation, it is easy to fall to the ground and cause the lens to be damaged. Hold the objective lens with the index finger and middle finger of the left hand, and then attach the objective lens with the right hand, so that even if it is not installed, it will not fall to the ground.
Second, the problem of correct light
Focusing is an important step when using a microscope. Some students turn an objective lens to the light-through hole while focusing, instead of using a low-power lens to focus the light as required. When turning the mirror, I like to use one hand, and often pull the mirror down. Therefore, teachers must emphasize the use of low magnification mirrors when instructing students. When the light is strong, use small apertures and flat mirrors, and when the light is weak, use large apertures and concave mirrors. The mirrors need to be turned with both hands. Until a uniformly bright circular field of view. Don't move the microscope casually after the light is aligned, otherwise the light will not enter the clear hole through the mirror accurately.
Third, the correct use of quasi-focus spiral
Using the quasi-focus screw to adjust the focal length and find the object image can be said to be the most important step in the use of the microscope and the most difficult step for the students. Students are very prone to the following errors during operation: one is to directly adjust the focus under a high magnification lens; the second is to keep looking at the field of view in the eyepiece regardless of whether the lens barrel rises or falls; the third is to not understand the critical value of the object distance. When the distance is adjusted to 2 ~ 3 cm, it is still adjusted upward, and the speed of rotating the quasi-focus screw is very fast. The first two error results often cause the objective lens to interfere with the mount and damage the mount or lens, while the third error is the most common phenomenon when students use the microscope. In response to the above errors, the teacher must emphasize to the students that the adjustment of the focal length must be lowered at the low magnification lens, first turn the coarse quasi-focus screw to slowly lower the lens barrel, and the objective lens is close to the slide, but be careful not to let the objective lens touch the glass In this process, the eyes should look at the objective lens from the side, and then look into the eyepiece with the left eye, and slowly adjust the coarse quasi-focus spiral in the reverse direction to make the lens barrel rise slowly until the object image is seen, and explain to the student Generally, the object distance of the microscope is about 1 cm, so if the object distance is more than 1 cm, but the object image is still not seen, it may be that the specimen is not in the field of view or the speed of the coarse quasi-focus spiral is too fast, and it should be adjusted at this time. Position the film, and then repeat the above steps. When a blurred object image appears in the field of view, it is necessary to use a fine quasi-focus spiral adjustment. Only in this way can the search range be narrowed and the speed of finding the object image can be increased.
Fourth, the problem of objective conversion
After using a low magnification lens instead of a high magnification lens, students often like to use their fingers to directly rotate the objective lens, which is more labor-saving, but it is easy to deflect the optical axis of the objective lens because the material texture of the converter is soft and the accuracy is high , Uneven thread force is easy to loosen. Once the thread breaks, the entire converter will be scrapped. Teachers should instruct students to hold the converter's lower rotating plate to convert the objective lens.
Five, the problem of correct use of eyes
When observing an object with a microscope, both eyes should be opened at the same time, and the left eye should look into the eyepiece. However, many students often fail to do this, and like to cover their right eyes with their hands or simply close their right eyes. This is not in line with the observation requirements of the experiment. This bad habit will cause fatigue in the left eye, and they ca n’t do it at the same time. Draw while observing. While pointing out this problem of the students, the teacher should demonstrate specifically, tell the students to keep the left eye as close as possible to the eyepiece, and the right eye to try to stare into the field of view. Such repeated training will meet the requirements of both eyes opening the observation at the same time. Or you can do the following exercises: open your eyes, use a piece of paper or a palm to stand between the two eyes, the nose in front of you, so that the left and right eyes cannot look at the opposite side, and then consciously look at the left first, then the right, so Do this 3 to 5 times a day, morning and evening, and learn in less than a week.
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