问题 探究题

小东学会了测小灯泡的功率后,想进一步探究:电流相同时,小灯泡功率跟电阻有什么关系?于是他利用如图甲所示的电路,选用分别标有“1.5V  0.25A”、“2.5V  0.3A”和“3.8V  0.3A”字样的小灯泡L1、L2、L3,测出它们在电流相同时的电阻和功率,来探究小灯泡功率与电阻的关系.    

(1)闭合开关前,滑动交阻器的滑片P应置于    _____ (选填“A“B”)端。  

(2)闭合开关后,他调节滑动变阻器的滑片P,使通过灯L1的电流为0.2A,再测出L1两端的电压,此时电压表示数如图乙为  _______ V,然后计算出此时灯L1的电阻是____Ω,实际功率是_____W。

(3 )他再分别更换灯L2、L3,闭合开关,调节滑动变阻器阻值,保持电流示数为0.2A 不变,计算出相应的电阻值与实际功率。小红认为:为了控制实验条件,小东每次实验都要换灯泡和调节滑动变阻器,这样的操作不够简便。对此你如何改进?

答案

(1)A  

(2)0.8 ;4 ;0.16

(3)可以将L1、L2、L3串联在同一电路中,就控制了电流一定

完形填空
阅读下面短文,根据所读内容在表格中的空白处填入恰当的单词。注意:每个空格只填一个单词。
Farmers and gardeners have long used greenhouses to extend the growing season in cold weather. Now, hoop houses are gaining popularity. Some hoop houses are rounded; others are shaped more like a traditional house.
A hoop house is basically a metal frame covered with plastic or other all-weather material. A common design looks like a high tunnel. Unlike a greenhouse, which uses a heating system, a hoop house is heated by the warmth of the sun.
Now, the United States Department of Agriculture has announced a program to help farmers who want to build hoop houses. The department has been supporting a project in Michigan. That state has a short growing season. As part of the research project, nine farmers were given materials and trained how to build and use a hoop house. The results showed that well-managed hoop houses can grow high-quality crops.
However, crops are not the only things that grow well. The research found that weeds grow faster in a hoop house. Weeding (除草), seeding and watering requires at least as much work as crops grown in the open air. The researchers also advise growers to add compost(堆肥) material to the soil in hoop houses to build nutrients.
Eliot Coleman is an organic farmer and a writer in Maine who has helped popularize the idea of four-season farming. His ideas about hoop houses sounded good to John Biernbaum in the Horticulture(园艺)Department at Michigan State University.
Professor Biernbaum tried hoop houses on the Student Organic Farm at Michigan State and had success. Project director David Conner says it was a "test drive(试车)" for the research on private farms. The agricultural economist points to the demand for locally grown crops. "People are hungry for good, fresh vegetables," he says.
          Topic
                 Hoop houses
 
Design
 
小题1:_________
·Like a high tunnel
·Some round ; others like a 小题2:        house.
Material
·Metal frame.
·Plastic or other all-weather material.
小题3:        
The warmth of the sun.
 
Research
project in
Michigan
 
The program
·It is 小题4:_________by the US Department of Agriculture.
·Michigan was chosen due to its short【小5题】_________season.
·Nine farmers were given materials and trained how to build
and use a hoop house.
·It is greatly 小题5:_________by the ideas from Eliot Coleman.
 
小题6:         
·High-quality crops can grow in well-managed hoop houses.
·Weeds also grow faster in hoop houses.
 
小题7:         
·Weeding, seeding and watering needs as much work as
naturally grown crops.
小题8:         should be added to the soil.
Significance
Demand for locally grown crops 小题9:_________further research
on private farms.
 
单项选择题