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A.LED灯具有单向导电性 |
B.一只LED正常工作的电压是220V |
C.LED灯工作时主要是将电能转化为内能 |
D.灯带中一只LED灯断路后其它灯还亮 |
A.![]() | B.![]() |
C.![]() | D.![]() |
A.在汽油机的压缩冲程中,内能转化为机械能 |
B.金属导体中自由电子定向移动的方向与电流方向相反 |
C.与丝绸摩擦过的玻璃棒带负电 |
D.机械效率越高的机械做功越快 |
![](https://img.xkw.com/dksih/QBM/editorImg/2023/3/19/ba81c5b4-cc52-4d66-b0fa-333162af9a53.png?resizew=132)
A.LED灯是用超导材料作成的 |
B.灯带中一只LED灯断路后其它灯还亮 |
C.LED灯工作时主要是将电能转化为内能 |
D.LED灯具有单向导电性 |
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/7/84543117-0169-4576-b2df-7e1a11254a37.png?resizew=222)
![](https://img.xkw.com/dksih/QBM/2017/9/19/1777280840032256/1780953822347265/STEM/2179007e7dcd4bfebe41cd03553254f2.png?resizew=141)
![](https://img.xkw.com/dksih/QBM/2017/8/21/1756740380958720/1770865221795840/STEM/737911ae-b748-4e17-b9a1-da4f51ae60cc.png?resizew=155)
A.A 验电器中有正电荷通过棒流向B,使B带正电荷 |
B.B验电器中有负电荷通过棒流向A,使B带正电荷 |
C.棒中有电流从B流向A,使B张角增大 |
D.棒中有电流从B流向A,使A张角增大 |
电子线路中有一种常用的器材叫二极管,在电路图中的符号如图所示.它在电路中的作用是:当电流从“+”极端流入时,二极管对电流的阻碍作用很小,相当于一个阻值很小的电阻,此时二极管可视为一段导线;当电流从“-”极端流入时,二极管相当于一个阻值很大的电阻,使电流几乎不能通过它,即电流几乎为零,此时二极管可视为绝缘体.
![](https://img.xkw.com/dksih/QBM/2017/8/20/1756401069375488/1770820065148928/STEM/31e8babd-2901-480c-8394-9cbb3a50de31.png)
因此,二极管可以视为—个由电流方向控制的开关,当电流从“+”极端流入时,相当于开关闭合,当电流从“-”极端流入时,相当于开关断开.
此外,二极管还有许多用途,比如:整流、限幅、续流、检波、阻尼、稳压等等.
二极管种类有很多,按照所用的半导体材料,可分为锗二极管(管)和硅二极管(
管).根据其不同用途,可分为检波二极管、整流二极管、稳压二极管、开关二极管、隔离二极管、肖特基二极管、发光二极管、硅功率开关二极管、旋转二极管等.按照管芯结构,又可分为点接触型二极管、面接触型二板管及平面型二极管.点接触型二极管是用一根很细的金属丝压在光洁的半导体晶片表面,通以脉冲电流,使触丝一端与晶片牢固地烧结在一起,形成一个“
结”.由于是点接触,只允许通过较小的电流(不超过几十毫安),适用于高频小电流电路,如收音机的检波等.面接触型二极管的“
结”面积较大,允许通过较大的电流(几安到几十安),主要用于把交流电变换成直流电的“整流”电路中.平面型二极管是一种特制的硅二极管,它不仅能通过较大的电流,而且性能稳定可靠,多用于开关、脉冲及高频电路中.
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A.方向向下 |
B.方向向上 |
C.为零,因为线圈处于水平位置 |
D.为零,因为ab段导线向上转动 |