题干

如图甲为一理想自耦变压器,输入端接交流稳压电源,其电压随时间变化关系如图乙所示.已知n1、n2的比值为2:1,负载电阻R的阻值为5Ω,下面正确的说法有(   )

A:负载电阻R消耗的电功率约为48W

B:通过负载电阻R的电流的有效值为22A

C:通过负载电阻R的电流的频率为100Hz

D:通过负载电阻R的电流的频率为25Hz

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答案(点此获取答案解析)

B

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    As I held my father's hands one night, I couldn't help but notice their calluses (老茧) and roughness. His hands tell the story of his life as a1, including all his struggles.

    One summer, I remember, a drought (旱灾) hit Ontario, turning it into a 2desert. On one of those hot mornings I was picking sweet com with my dad to fill the last3from the grocery store. Fifty dozen was all we needed, which4took twenty minutes. That morning, however, the process didn't 5quickly. After forty minutes of aimlessly walking in the field, we6 needed twenty dozen. I was completely frustrated (挫败的) and7. Dropping the basket heavily, I declared, “If the store wants its last twenty dozen, they can pick it themselves”. Dad8. “Just think, my little girl, only ten dozen left for each of us and then we're9.” Such is Dad----whatever problem he 10 he never gives up.

    11  the bad effects of the drought were felt all over our county. It was a challenging time for everyone,12Dad remained optimistic (乐观的). He 13to be grateful for other things like good health and food on our plates. Only then did I truly begin to 14Dad and his faith that guided us through the hard times.

    Dad is also a living example of real 15  From dawn to dusk, he works countless hours to 16our family. He always puts our happiness 17his own and never fails to cheer me on at my sports games 18his tiredness after long days. His loving and selfless nature has encouraged me to become more sympathetic (有同情心的) and19, putting others first.

    Dad, the life 20I have learned from you will stay with me forever. You are my father, teacher, friend and, most importantly, my hero.