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电磁式打点计时器的结构简单、价格低廉,是中学物理实验教学中应用最广泛的仪器之一。实验中产生的误差较大是电磁打点计时器主要缺点。究其原因:首先是电磁打点计时器的振针在打点的过程中会对记录纸带的运动产生阻碍作用,使纸带的运动速度变慢;其次是电磁打点计时器由降压后的交流电驱动,其打点的时间间隔为交流电的一个周期,即0.02s,对于许多实验来说,这个时间间隔太短了。例如在测定匀变速运动的加速度时,一般取0.1s作为计时单位。故实验中需要将打点计时器的振针在记录纸带打的名称为记录点,而将从记录点中人为选择出来的,用于计时的点称为计数点。纸带上每5个记录点中仅有一个为计数点,即计数点的间隔为0.02s×5=0.1s。由此可见,多数记录点
The electromagnetic striking timer has a simple structure and low price, and is one of the most widely used instruments in the middle school physics experiment teaching. The larger error produced in the experiment is the main drawback of the electromagnetic strike timer. The reason is as follows: first, the vibrating needle of the electromagnetism timer will hinder the movement of the recording paper during the process of dot punching, which will slow down the speed of the paper strip; secondly, the electromagnetism timer will be replaced by the alternating current after depressurization. Drive, the time interval of its dribbling is one cycle of alternating current, namely 0.02s, for many experiments, this time interval is too short. For example, when measuring the acceleration of a uniform speed change motion, 0.1s is generally taken as the timing unit. Therefore, in the experiment, the name of the vibrating needle of the dotting timer on the recording paper tape needs to be the recording point, and the point selected for the timing from the recording point by the hand is called the counting point. Only one of every 5 recording points on the tape is the counting point, ie the interval of the counting points is 0.02 s×5=0.1 s. This shows that most of the records