如图所示为一种磁性加热装置，其关键部分由n根间距相等的平行金_爱下问搜题

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问题计算题

如图所示为一种磁性加热装置，其关键部分由n根间距相等的平行金属条两端焊接在两个等大的金属圆环上，成鼠笼状。每根金属条的长度为l，电阻为R，金属环的直径为D、电阻不计。图中虚线所示的空间范围内存在着磁感强度为B的匀强磁场，磁场的宽度恰好等于“鼠笼”金属条的间距，当金属环以角速度ω绕过两圆环的圆心的轴OO′旋转时，始终有一根金属条在垂直切割磁感线。“鼠笼”的转动由一台电动机带动，这套设备的效率为η，求电动机输出的机械功率。

答案

处于磁场中的金属条切割磁感线的线速度为

①

产生的感应电动势为 ③

通过切割磁感线的金属条的电流为 ②

磁场中导体受到的安培力为 ②

克服安培力做功的功率为 ③

电动机输出的机械功率为 ②

联立以上各式解出 ②

单项选择题

真核生物DNA复制的主要酶是（）

A.DNA聚合酶β

B.DNA聚合酶γ

C.DNA聚合酶δ

D.DNA聚合酶ε

E.DNA聚合酶α

填空题

Beauty has always been regarded as something (36) . Almost everyone thinks attractive people are happier and healthier, have better marriages and have more (37) occupations. Personal (38) give them better advice for finding jobs. Even judges are softer on attractive (39) . But in the executive circle, beauty can become a (40) . While attractiveness is a positive factor for a man on his way up the executive (41) , it is harmful to a woman. Handsome male executives were (42) as having more integrity than plainer men; effort and ability were thought to (43) for their success. Attractive female executives were considered to have less integrity than unattractive ones; their success was attributed not to ability but to factors such as luck. All unattractive women executives were thought to have more integrity and to be more capable than the attractive female executives. Interestingly, though, (44) . Why are attractive women not thought to be able.’ An attractive woman is perceived to be more feminine and an attractive man more masculine than the less attractive ones. (45) . This is true even in polities. A study was made on the attractiveness of political candidates. (46) .