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有一次在物理统考时,我曾出了这样的一道光学题:用凸透镜在屏上得到一个放大一倍的物体的象。把透镜向屏移36厘米,象就缩小了1/2倍,求透镜的焦距。结果大部分学生的答案是焦距为24厘米,少数学生答案是54厘米,显然焦距为54厘米的答案是正确的,而焦距为24厘米的结果是错误的。可是多数学生为什么得出错误结论?仔细看看学生的答卷,发现凡得出焦距为24厘米的学生,放大率都是按照2计算的。问题的症结在于对放大一倍这个术语的理解不
One time in the physical examination, I had this optical problem: Use a convex lens to get an image of a doubled object on the screen. Move the lens 36 cm toward the screen, and the image is reduced by a factor of 1/2. Find the focal length of the lens. Results The answer for most students is a focal length of 24 cm. The answer for a few students is 54 cm. Obviously the answer with a focal length of 54 cm is correct, and the result with a focal length of 24 cm is wrong. But why do most students make the wrong conclusion? Take a close look at the student’s response and find that for students who have a focal length of 24 cm, the magnification is calculated as 2. The crux of the problem lies in the lack of understanding of the term