如图甲所示，理想变压器原、副线圈的匝数比为10∶1，b是原线圈的中心抽头，图中电表均为理想的交流电表，定值电阻R＝10Ω，其余电阻均不计，从某时刻开始在原线圈c、d两端加上如图乙所示的交变电压，则下列说法中正确的是
A．当单刀双掷开关与a连接时，电压表的示数为22V
B．当单刀双掷开关与a连接且t＝0.01s时，电流表示数为零
C．当单刀双掷开关由a拨向b时，原线圈的输入功率变大
D．当单刀双掷开关由a拨向b时，副线圈输出电压的频率变为25Hz
AC
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| One effective way of destroying happiness is to look at something and focus on even the smallest fault. It’s like looking at the tiled (铺瓦的) ceiling and concentrating on the space where one tile is 1 Once I heard a bald man said, “whenever I enter a room 2 I see is hair.” Once you’ve 3 what your missing tile is, explore whether acquiring it will 4 make you happy. Then do one of the three things: get it, replace it with a different 5 , or forget about it and 6 the tiles in your life that are not missing. We all know people who have a relatively 7 life, yet are essentially unhappy while people who have suffered a great deal but 8 remain happy. The first 9 is gratitude. All happy people are 10 . Ungrateful people cannot be happy. We tend to think that being unhappy leads people to 11 , but it’s truer to say that complaining leads to people becoming unhappy. The second secret is 12 that happiness is a byproduct (副产品) of something else. The most obvious 13 are those pursuit (追求) that give our lives purpose - anything 14 studying insects to playing baseball. The more passions we have, the more happiness we are 15 to experience. Finally, the belief that something permanent goes beyond us and that our 16 has some larger meaning can help us to feel happier. We 17 a spiritual faith, or a philosophy, it should 18 this truth: if you choose to find the 19 in every situation, you will be blessed, and if you choose to find the awful, you will be cursed. As with happiness itself, this is 20 your decision to make. | ||||
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