(4分)如图所示，用某种频率的单色光a照射光电管阴极K，电流计G的指针发生偏转，而用另一频率的单色光b照射光电管阴极K时，电流计G的指针不发生偏转，那么a光的频率 b光的频率(填“大于”、“等于”或“小于”)，若增加b光的强度 (选填“会”或“不会”)使电流计G的指针发生偏转。
大于，不会。
题目分析：产生光电效应的条件是照射金属的光子频率大于或等于金属的极限频率，由题意可知，单色光a照射光电管阴极K，能使电流计G的指针发生偏转，说明发生了光电效应，且电路完好，而单色光b照射光电管阴极K时，电流计G的指针不发生偏转，即此时不能产生光电效应，所以a光的频率大于了b光的频率，能否发生光电效应现象，仅与照射光的频率有关，与光的强度无关，因此增加b光的强度同样不会使电流计G的指针发生偏转。
| The field of medicine has always attracted its share of quacks and charlatans — disrepu-table women and men with little or no medical knowledge who promise quick cures at cheap prices. The reasons why quackery thrives even in modem times are easy to find. To begin with, pain seems to be a chronic human condition. A person whose body or mind "hurts" will often pay any amount of money for the promise of relief. Second, even the best medical treatment cannot cure all the ills that beset men and women. People who mistrust or dislike the truths that their physicians tell them often turn to more sympathetic ears. Many people lack the training necessary to evaluate medical claims. Given the choice between (a) a reputable physician who says a cure for cancer will be long, expensive and may not work at all, and (b) a salesperson who says that several bottles of a secret formula "snake oil" will cure not only cancer but tuberculosis as well, some individuals will opt for "snake oil". Many "snake oil" remedies are highly laced with alcohol or narcotic drugs. Anyone who drinks them may get so drunk or stoned that they drown their pains in the rising tide of pleasant intoxication. Little wonder that "snake oil" is a popular cure-all for minor aches and hurts! But let there be no misunderstandings. A very few "home remedies" actually work. However, most remedies sold by quacks are not only useless, but often can be harmful as well. |
To evaluate medical claims, one must______.
A．turn to reputable doctors
B．make an adequate choice
C．have the necessary training
D．disbelieve promise of relief