题目

小明在探究“电流与电阻的关系”实验中，采用如图甲所示电路，选用电压恒为4V的电源。多次改变电阻R的阻值，并记录对应的电流表示数，得到如图乙所示的电流随电阻R变化的图象。求：(1)实验过程中，电压表示数；(2)当电阻R=25Ω时，滑动变阻器接入电路的阻值为多少？ 答案：【答案】(1)2.5V；(2)15Ω【解析】解：(1)探究电流与电阻的关系，须控制电阻两端的电压不变，图乙中通过电阻的电流与电阻的阻值成反比，当电阻阻值为10Ω时，电流为0.25A，则实验过程中，电压表示数为U=IR=0.25A×10Ω=2.5V(2)滑动变阻器与定值电阻串联，由图乙可知，当电阻R'=25Ω时，电路中电流为0.1A，则电 阅读理解 　　What will people die of 100 years from now? If you think that is a simple question, you have not been paying attention to the revolution that is taking place in bio-technology(生物技术)．With the help of new medicine, the human body will last a very long time．Death will come mainly from accidents, murder and war．Today's leading killers, such as heart diseases, cancer, and aging itself, will become distant memory． 　　In discussion of technological changes, the Internet gets most of the attention these days．But the change in medicine can be the real technological event of our times．How long can humans live? Human brains were known to decide the final death．Cells(细胞)are the basic units of all living things, and until recently, scientists were sure that the life of cells could not go much beyond 120 years because the basic materials of cells, such as those of brain cells, would not last forever．But the upper limits will be broken by new medicine．Sometime between 2050 and 2100, medicine will have advanced to the point at which every 10 years or so, people will be able to take medicine to repair their organs(器官)．The medicine, made up of the basic building materials of life, will build new brain cells, heart cells, and so on---in much the same way our bodies make new skin cells to take the place of old ones． 　　It is exciting to imagine that the advance in technology may be changing the most basic conditional human existence, but many technical problems still must be cleared up on the way to this wonderful future． (1) According to the passage, human death is now mainly caused by ________． [　　] A． diseases and aging B． accidents and war C． accidents and aging D． heart diseases and war (2) In the author's opinion, today's most important advance in technology lies in ________． [　　] A． medicine B． the internet C． brain cells D． human organs (3) Humans may live longer in the future because ________． [　　] A． heart disease will be far away from us B． human brains can decide the final death C． the basic materials of cells will last forever D． human organs can be repaired by new medicine (4) We can learn from the passage that ________． [　　] A． human life will not last more than 120 years in the future B． human have to take medicine to build new skin cells now C． much needs to be done before humans can have a longer life D． we have already solved the technical problems in building new cells．