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问题 计算题

美的CFXB型“220V 440W”电饭煲的原理如图所示，它有高温烧煮和焖饭保温两挡，其铭牌如下表所示。

电饭煲容量2L
额定电压220V
高温煮饭功率880W
焖饭保温功率110W
 

（1）当开关S闭合时，电饭煲处于高温烧煮挡还是焖饭保温档？且当电饭煲处于高温烧煮挡时工作10min消耗的电能为多少？

（2）电热丝R1和R2的阻值各是多大？

（3）当电饭煲在正常焖饭保温时R1消耗的电功率是多大？

答案

（1）5.28×105J；（2）55Ω，385Ω （3）13.75w

由电功公式可求得消耗的电能；由功率公式可求得电热丝的阻值； 由P1=I2×R1可求出电功率；解：（1）当开关S闭合时，电饭煲处于高温烧煮挡（1分）；

W=P高温×t=880w×10×60s=5.28×105J（1分）；

（2）当开关S闭合时，电饭煲处于高温烧煮挡，此时

R1=U2/P高温=（220V）2/880w=55Ω（1分）

当开关S断开时，电饭煲处于焖饭保温挡，此时R1和R2串联在电路中则：

R总=U2/P保温=（220V）2/110w=440Ω（1分）

R2=R总-R1=440Ω-55Ω=385Ω（1分）

（3）当电饭煲处于焖饭保温挡时，

I=P保温/U=110w/220V=0.5A（1分）

P1=I2×R1=（0.5A）2×55Ω=13.75w（1分）

填空题

透镜有 _________ 透镜和 _________ 透镜两种，透镜是利用光的 _________ 规律工作的．
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完形填空

“Everything happens for the best,” my grandmother said whenever things weren’t going my way. “Don’t worry, one day your luck (1) _____________(change). ”

Grandmother was right, as I discovered after graduating from college. I had decided to be sports announcer (广播员) in a radio station, so I (2) _____________ ( go) to Shanghai and knocked on the door of every station. But I got refused every time.

In one station, a kind lady said my problem was short of experience. “ Get some work with a small station and (3)_______________(work) your way up ,” she said.

I couldn’t get a job there, either. Then my dad told me a businessman had opened a company and needed someone (4 )_____________ ( manage) the sports center. But again, I didn’t get the job.

I felt really down. “Your luck will change,” Granny reminded me. I tried another radio station in Beijing. But the owner, a nice man, told me he already had someone.

As I left his office, I asked, “ How can someone be a sports announcer if he ( 5 )_____________(not, get) a job in a radio station?”

I ()______________( wait) for the elevator when I heard the man call, “What was that you said about sports? Do you know anything about football?” I (7)______________(put) in front of a microphone and asked to imagine I was commenting (评论) on a football game. “Now you (8)____________ (watch) the football game between Lu Neng and Shen Hua. . . ”

On my way home, Granny’s words came back to me, “One day your luck will change, boy. And when it (9 ) ____________( happen) , it’ll feel twice as good because of all the disappointment (失望) you (10) ____________ ( have) . ” At that moment I knew just what she meant.
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