题目

It is the second-brightest object in our night sky after the moon. It is one of man's the greatest scientific achievements. It's the International Space Station (ISS) that moves around Earth. Nov 20 is the stations’ 20th birthday. In 1998, the first piece of the ISS was sent into space. Since then, 230 people from 18 countries have visited it. Five space agencies –those of the United States, Russia, Canada, Europe and Japan- worked together to build it. Weighing about 450 tons, it contains many different parts.Generally, the ISS holds three to six people at one time. Astronauts living ther如图（甲）为小型旋转电枢式交流发电机的原理图，其矩形线圈在匀强磁场中绕垂直于磁场方向的固定轴OO′按如图所示方向匀速转动，线圈的匝数n=100、电阻r=10Ω，线圈的两端经集流环与电阻R连接，电阻R=90 Ω，与R并联的交流电压表为理想电表。 在t＝0时刻，线圈平面与磁场方向平行，穿过每匝线圈的磁通量随时间t按图（乙）所示正弦规律变化。（取π＝3.14） 求：（1）交流发电机产生的电动势的最大值；（2）从t＝0时刻开始计时，线圈转过600时线圈中感应电流瞬时值及回路中的电流方向；（3）电路中交流电压表的示数；（4）线圈从图示位置转过90°过程中，通过线圈的电量和整个回路的焦耳热。