题目

如图是用伏安法测电阻的电路图，电流表电阻可忽略不计，只考虑电压表本身的电阻，那么A. 测量值等于电阻的实际值B. 测量值小于电阻的实际值C. 测量值大于电阻的实际值D. 测量值加电压表的内阻值等于电阻的实际值 答案：【答案】B【解析】根据，测量电阻时，应该测量电阻两端的实际电压和通过电阻的实际电流；由图可知，电流表实际测量的是通过待测电阻和电压表的总电流，即电流偏大，而电压表是与电阻并联连接，测量的电压是准确的；即电压准确，而电流偏大，根据可知，电阻的测量值小于实际值．故选B．18．听下面一段独白，回答第13～15三个小题．13．How many visiting hours are there in a day？A．One．B．Two．C．Three．14．What do we know about the hospital？A．People can visit patients at 3 p．m．B．Smoking is not allowed in the hospital．C．All visitors are welcome at visiting hours．15．What's the purpose of the speech？A．To introduce the hospital．B．To welcome the patients．C．To tell the hospital rules．