[题目]目前有些居民区内楼道灯的控制.使用的是一种延时开关.该延时开关的简化原理如图所示.图中D是红色发光二极管(只要有很小的电流通过就能使其发出红色亮光).R为限流电阻.K为按钮式开关.虚线框内S表示延时开关电路.当按下K接通电路瞬间.延时开关触发.相当于S闭合.这时释放K后.延时开关S约在1 min后断开.电灯熄灭.根据上述信息和原理图.我们� 题目和参考答案——青夏教育精英家教网—

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【题目】目前有些居民区内楼道灯的控制，使用的是一种延时开关。该延时开关的简化原理如图所示。图中D是红色发光二极管（只要有很小的电流通过就能使其发出红色亮光），R为限流电阻，K为按钮式开关，虚线框内S表示延时开关电路，当按下K接通电路瞬间，延时开关触发，相当于S闭合，这时释放K后，延时开关S约在1 min后断开，电灯熄灭。根据上述信息和原理图，我们可推断：

按钮开关K按下前，发光二极管是________（填“发光的”或“熄灭的”），按钮开关K按下再释放后，电灯L发光持续时间约________min。这一过程中发光二极管是________。限流电阻R的阻值和灯丝电阻RL相比，应满足R________RL的条件。

【答案】发光的 1 熄灭的

【解析】开关K按下前，S为断开，有电流经过发光二极管，故发光二极管是发光的。当按下开关K后，延时开关S闭合，二极管和R被短路，二极管不发光，由于延时开关S约1 min后断开，故电灯L能持续发光1 min，由于R为限流电阻，且二极管只要有很小的电流通过就能发光，故应满足RRL。

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