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【题目】一块数码相机中用的锂电池的电压为3．6 V，容量为1 000 mA·h（相当于用1 000 mA的电流可放电1 h，用500 mA的电流可放电2 h，以此类推）。当关闭液晶屏时可拍摄照片400张左右，则每拍一张照片所消耗的电能约为________J；当打开液晶屏时可拍摄照片150张左右，则每拍一张照片液晶屏消耗的电能约为________J。

【答案】32．4；54

【解析】电源输出的总电能

E＝UQ＝UIt＝3．6×1×3 600 J＝12 960 J

关闭液晶屏时，每拍一张照片消耗的电能E1＝＝32．4 J

打开液晶屏时，每拍一张照片消耗的电能E2＝＝86．4 J

每拍一张照片液晶屏消耗的电能E3＝E2－E1＝86．4 J－32．4 J＝54 J

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