题干

某同学在做“调节灯泡亮度”的电学实验时,电路如图所示,电源电压恒为6V,电流表的量程为“0﹣0.6A”电压表量程“0﹣3V”,滑动变阻器的规格为“20Ω 2A”,灯泡L标有“3V 0.9W”字样(忽略灯丝电阻变化),在实验中为了保证所有元件的安全,下列判断不正确的是(   )

A:该电路中,变阻器R接入电路的阻值变化范围为0﹣20Ω

B:该电路消耗的总功率的变化范围为1.2W﹣3.6W

C:该电路中,电流表示数的变化范围为0.2A﹣0.6A

D:该电路中,电灯消耗功率的变化范围为0.4W﹣0.9W

上一题 下一题 0.0难度 选择题 更新时间:2019-10-18 02:04:29

答案(点此获取答案解析)

A,B,C

同类题4

阅读理解

    It was a cold winter. The wind blew all night and the snow was blinding. When morning came, my three children and I got up and made our way to the windows. As we looked out the window, we saw that the henhouse was gone. Our three hens had been blown away.

    I looked at the emptiness outside. Then I saw all three chickens sat around the edge of a white bucket. How was this violent wind not blowing them into the field beyond? I quickly pulled on long snow pants and heavy winter coat, wrapped a scarf and stuck my feet into very large boots .

    I shouted at the wind as it blew. I was alone, save for my children. They stared out the window into the vast white sea of snow, their eyes peeled for any sign of movement. Outside I heard the sound of my boots as I walked against the wind.

    The snow circling around me, I steadily made my way to the soft cluck-cluck-cluck sound my hens always made. When I reached them, I saw that their little feet were holding on to the edge of the bucket, heads bent forward and away from the wind. I gently lifted each hen and put it carefully into the warm inside. Then I began the freezing walk back to the small shed directly behind our house. One by one I laid my chickens on the cold floor, and they began to cluck softly.

    As I shut the shed doors, my eyes went directly to the window where my children were watching. They jumped up and down cheering, and so did I! I wasn't some dragon slayer (屠龙者) from a fairy tale. I was simply a mom, but the look on my children's faces told me that they thought I was a hero mom.