巧测凹透镜焦距四法吴俊良（江苏省大丰市第二中学，２２４１００）由于凹透镜不能成实像被光屏接收，因此无法直接测量它的焦距．下面介绍四种间接测量法，供读者参考．方法一器材光具座、平行光源、凹透镜、光屏、纸条和带有毫米的刻度尺．原理凹透镜焦点定义和相似三角... Four methods for measuring the focal length of concave lenses Wu Junliang (secondary school, Dafeng City, Jiangsu Province, 224100) Since the concave lens cannot be received by the light screen, it cannot measure its focal length directly. The following introduces four indirect measurement methods for readers’ reference. Method A equipment optical bench, parallel light source, concave lens, light screen, paper strip and scale with millimeter. Principle Concave Lens Focus Definition and Similarity Triangle...