1 电灯泡的瓦数是a,那么照明7h的用电量是7a÷1000度电;
2 用一个15W灯泡,如果每天照明4h,则每月(30天)共用电15x4x30÷1000=1.8度电
上述要点:1度电=1千瓦小时=1000Wh
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