问题 选择题

如图所示是某种型号的电热毯的电路图,电热毯接在交流电源上,通过装置p使加在电热丝上的电压的波形如图所示.此时接在电热丝两端的交流电压表的读数为(  )

A.110V

B.156V

C.220V

D.311V

答案

由图象可知该交变电流的周期T=2×10-2s

可分两段0-0.01s和0.01-0.02S

根据有效值的定义可得

Um
2
2
R
  
T
2
+0=
U2
R
T,U=
Um
2
=
311
2
v=156v

故答案为B

材料分析题

改革开放20多年来,我国综合国力显著增强,经济增长速度名列世界首位。但是在经济如何发展的问题上一直存在两种倾向:一种认为只需坚持独立自主,自创品牌;另一种则认为只需坚持对外开放,全面引进。请谈谈你的看法。

                                                                                                                                                              

                                                                                                                                                             

                                                                                                                                                              

                                                                                                                                                              

                                                                                                                                                            

选择题