拉伸法测量金属丝杨氏模量拓展实验设计及实践研究

Experimental Design and Practical Study on Extending Young’s Modulus Measurement of Wire by Tensile Method

摘要: 拉伸法测量金属丝杨氏模量实验是大学物理实验课程的重要组成部分，通过对金属丝微小形变量的测量掌握光杠杆的原理是实验中的重要内容。光杠杆是以镜子作为支点，光路作为放大臂的重要放大测量装置，广泛的应用于各种精密测量中。光杠杆的放大臂常常称为光杠杆镜面到标尺的距离，这段距离究竟是光杠杆镜面到标尺的垂直距离还是光杠杆镜面到标尺的直线距离常常引起学生困扰。以往的实验研究大多关注如何提高光杠杆放大率或者提高光杠杆的探测精度，很少涉及来清楚的展示光杠杆的放大臂具体指的是那段距离。本文针对学生常常混淆的光杠杆放大臂测量，设计了大角度光杠杆实验作为杨氏模量实验的拓展实验。通过将望远镜和尺子分开，通过测量在不同尺子和光杠杆中垂线夹角时金属丝的伸长量来区分光杠杆放大臂的真正长度。经过多次实验，证实在不同尺子和光杠杆中垂线夹角时金属丝的伸长量基本是相同的，变化不超过0.6%，非常清楚的示意出光杠杆镜面与尺子的垂直距离才是光杠杆放大臂的真正长度。经过调研，通过拓展实验学生清楚的了解光杠杆的放大臂，更加深入的掌握了测量原理，并且熟练了望远镜的操作。

Abstract: The experiment of measuring young’s modulus of metal wire by tensile method is an important part of college physics experiment course. In addition, it is important to master the principle of light lever by measuring the tiny deformation of metal wire in the experiment. The light lever is an important magnifying measuring device using a mirror as a fulcrum and an optical path as a magnifying arm, which is widely used in various precision measurements. The magnification arm of the light lever used to be often called the distance from the mirror of the light lever to the scale. Whether this distance is the vertical distance from the mirror of the light lever to the scale or the straight distance from the mirror of the light lever to the scale often causes students to be troubled. Most of the previous experimental studies have focused on how to increase the magnification of the light lever or improve the detection accuracy of the light lever, but it is not yet possible to show clearly the real distance of the magnification arm. In this paper, a large Angle light lever experiment is designed as an extension of Young’s modulus experiment. The true length of the optical lever amplifying arm is distinguished by separating the telescope from the ruler and measuring the elongation of the wire at the Angle between perpendiculars of different rulers and the optical lever. After many experiments, it is proved that the elongation of the metal wire is basically the same at the Angle between the vertical line of different rulers and the optical lever, and the change is not more than 0.6%. It clearly indicates that the vertical distance between the mirror of the light lever and the ruler is the real length of the optical lever magnifying arm. After investigation, the students clearly understood the amplification arm of the optical lever, grasped the measurement principle more deeply, and became proficient in the operation of the telescope through expanding the experiment.