题目

正弦交流电的电压随时间变化的规律如图所示。由图可知（ ）A.该交流电的电压的有效值为B.该交流电的频率为C.该交流电的电压瞬时值的表达式为D.若将该交流电压加在阻值为的电阻两端，则电阻消耗的功率是 答案：【答案】B【解析】A．由图可知，交流电的最大值为Um=100V，有效值为，A错误；B．由图可知，周期为0.04s，周期和频率公式，可得频率为，B正确；C．由公式，该交流电的电压瞬时值的表达式为，C错误；D．若将该交流电压加在阻值为的电阻两端，则电阻消耗的功率是D错误。故选B。短文改错假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。删除：把多余的词用斜线（╲）划掉。修改：在错的词下划一横线，并在该词下面写出修改后的词。注意：1.每处错误及其修改均仅限一词；2.只允许修改10处，多者（从第11处起）不计分。My soccer coach retired in last week. I wanted to do anything special for him at his retirement party. My mum makes the better biscuits in the world, so I decide to ask her for help. Mum taught me some basic step of baking. I insisted on doing most of the baking myself. I thought the biscuits were really well. My only mistake was that I dropped some on the floor after I was packing them up.At a party, my coach, with a biscuit in his mouth, asked surprisingly who made them and joked, “I might have to retire again next year just get some more of these biscuits.”My favorite picture at the party is of my coach and me enjoy the biscuits with happy laughter!