小明家中有40W日光灯5盏，25W白炽灯4盏，100W彩电、1200W空调、70

问题填空题

小明家中有40W日光灯5盏，25W白炽灯4盏，100W彩电、1200W空调、700W电饭锅、1000W电水壶各一只，他应选择额定电流等于或稍大于______A的保险丝接在进户线上．目前我市已实行新的分时电价政策，8：00到21：00电价为0.55元/度，其余时间电价为0.30元/度，若他家平均每天用电水壶烧水1h，小明将烧水时间由中午改在21：00以后．这样，一个月（30天）他家能节约电费______元．

答案

当小明家中得这些用电器同时工作时，

其总电流为：I=

=5×

40W

220V

+4×

25W

220V

100W

220V

1200W

220V

700W

220V

1000W

220V

=15A．

W=Pt=1kw×30h=30kw•h，小明烧水时间在21：00以前，

此时电费为30kw•h×0.55元/度=16.5元；

当小明烧水时间改在21：00以后，此时电费为30kw•h×0.3元/度=9元；

则他家能节约电费；16.5元-9元=7.5元．

故答案为：15；7.5．

完形填空。
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