题干

物理学研究中常常用到“控制变量法”、“等效法”、“类比法”等科学方法。在下列研究实例中运用了控制变量法的是(    )

A:研究电流的形成原因时将电流与水流比较从分析水流的形成入手来分析电流的形成

B:研究电流的大小时根据电流产生的效应大小来判断电流的大小

C:研究多个电阻组成的电路时求出电路的总电阻用总电阻产生的效果来代替所有电阻产生的总效果

D:研究电流与电压的大小关系时保持电阻大小不变改变电阻两端的电压值观察电流如何随电压变化而变化

上一题 下一题 0.0难度 选择题 更新时间:2019-10-29 11:55:34

答案(点此获取答案解析)

D

同类题5

    阅读下面短文,从每小题所给的A、B、C、D四个选项中选出最佳选项。

A

    A taxi company in one of Japan's big cities is introducing silent taxi drivers.Miyako Taxi,which is based in Kyoto,showed the new idea in March.The business is recently operating five "Silent Taxis" across the city.

    The cars look like any ordinary taxi,but a notice written on the back of the passenger seat tells passengers that they have entered one of the new silent cars.Drivers will offer a greeting when their passenger enters the car,and after making sure the route(路线)they will not start small talks.The drivers are only allowed to take their part in a conversation,only if they are spoken to first.Of course,they are also allowed to communicate in emergency(紧急的) situations.

    While introducing the idea to the public,a spokesman from Miyako Taxi said,"This service is currently in a trial(试验)period.It is introduced in order to create an in-car environment that provides the most comfortable ride for our passengers through reducing the driver's speaking."

    According to reporters from Japan Today,an online newspaper based in Tokyo,the taxi company made the decision after hearing reports from passengers that they felt bored to be forced to chat with their drivers.

    At the end of the trial period,the company will see how popular the silent taxis are with passengers before deciding whether to roll it out across more of their drivers or not.