对北京市2015年高考理综第24题的思考

THINKING OF THE 24^(TH) QUESTION IN THE SCIENCE INTEGRATED PAPER FOR THE UNIVERSITY ENTRANCE EXAMINATION OF BEIJING IN 2015

2015年北京高考物理卷立意新颖,注重理论联系实际,其中第24题涉及光电池的电动势和内阻问题,对于光电池是中学教学较少讨论过的问题,题目标准答案使用了借助光电池伏安特性曲线的方法求解光电池的电动势和内阻.本文针对标准答案的解法讨论了当光电池入射光照射时逸出光电子的初动能分布不同时,光电池的伏安特性曲线也不相同,因此必须交代逸出光电子的初动能分布规律,才可以确定光电池的伏安特性曲线,并进一步求解电源的电动势和内阻.文章还讨论了怎样的光电子初动能分布规律,才可以使光电池的伏安曲线为线性.

The physics paper of university entrance examination of Beijing in 2015 is novel and combines theory with practice. The 24th problem is about the electromotive force and internal resistance of photocell, which is scarcely discussed in middle school teaching. The standard answer of the problem uses the volt-ampere characteristic curve of photocell to calculate its electromotive force and internal resistance. Concerning the solving method of the standard answer, this study discusses that the volt-ampere characteristic curves of photocell show difference i{ distributions of the initial kinetic energy of the escape photoelectrons are different when the photocell is illuminated by an incident ray. Thus, the volt-ampere characteristic curve of photocell can only be determined after knowing the distribution of the initial kinetic energy of the escape photoelectrons. Then the electromotive force and internal resistance of the photocell can further be calculated. The study also discusses which kind of distribution of the photoelectrons＇ initial kinetic energy can result in such a linear volt-ampere curve.