9. 解:t=20min=1200s20min消耗的电能:W=Pt=800×1200=960000(J)若消耗的电能全部转化为热,则 Q=W=960000J答:略。10.解:t=1h=3600s消耗的电能为:W=I²Rt=0.5²×440×3600=396000(J)若消裤察耗的电能全部转化哗悉为热,则胡芦茄 Q=W=396000J答:略。