1.W = 40w * 30min = 40w * 1800s = 7200J
W = 40w * 30min = 0.04w * 0.5h = 0.02kw·h
2.每天消耗 250w * 3h = 0.25kw *3h = 0.75kw·h
每月则 0.75kw·h * 30d = 22.5kw·h
3.一节课40分钟,
总功率P=40W×15=0.04kW×15=0.6kW,
而t=40min=2/3h
W=Pt=0.6kW×2/3h=0.4kW.h
4、(1):t=30min=1800s,W=0.6kW.h=2160000J,
P=W/t=2160000J/1800s=1200W
(2)、P=1200W,t=2min=120s
W=Pt=1200W×120s=144000J
W=120/3000=0.04kW.h=144000J,t=1min=60s
P=W/t=144000J/60s=2400W