题干

电压力锅是一种新型家用电器,集高压锅与电饭锅优点于一体,既安全又环保。图是某型号电压力锅工作电路简图,右表是其部分参数。其中R2是主加热器,R1是保压加热器。接通电路后,开关S自动与触点b接通,开始加热。当锅内温度达到105℃时,开关S自动与b断开,并与触点c接通,开始保压,此时锅内水温不变,且未沸腾。现将3L初温为25℃的水 加入压力锅中,接通电路使其正常工作30min。已知消耗的电能有90%被有效利用,水的比热容为4.2×103J/(kg·℃)。求:
 
(1)电压力锅在加热状态时的电流。
(2)电压力锅多少秒后开始保压?
(3)电压力锅在此30min内消耗的电能。

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答案(点此获取答案解析)

解:(1)当压力锅处于加热状态时,R1、R2并联同时工作,
根据P=UI,所以加热状态时电流I==4.5A;
(2)3L水的质量m

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