题目

正方形导线框abcd，匝数为10匝，边长为20cm，在磁感强度为0.2T的匀强磁场中围绕与B方向垂直的转轴匀速转动，转速为120r/min．当线框从平行于磁场位置开始转过90°时，线圈中磁通量的变化量是            wb，线圈中磁通量平均变化率为                                                                            wb/s，平均感应电动势为          V．                                                 假如英语课上老师要求同学们交换修改作文，请你修改你同桌写的一篇作文。文中共有10处语言错误， 要求你在错误的地方增加、删除或修改某个单词。 增加：在缺词处加一个漏字符号（∧），在其下面写上该加的词。        删除：把多余的词用斜线（\）划掉。        修改：在错的词下划一横线，并在该词下面写上修改后的词。        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11处起）不记分。 例如：It was very nice to get invitation to spend  ∧  weekend with you．Luckily ﹨   the I was completely free then, so I’ll  to  say “yes”．I’ll arrive in Bristol at am around 8 pm in  Friday evening． on Dear Peter,      I’m writing to ask whether you are able to give me a favor．I want to have a pen pal, especially a girl in her early twenty, and with interests similar to mine．In my mind, she was someone who is interested in travelling and swimming．Beside, it would be better for her to have a pet dog as I have kept one at home for some times． With such a pen pal, I think I can share with him our travelling experiences, the way in that we take care of pets, or whatever we have in common．But I believe I will improve my English doing so and learn more about her country． I look forward to hear from you． Best regards, Yours Li Hua