07. Sähkölaitteen teho ja energian kulutus

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7-2
a) 19V, 2,1A
b) 40W
c)
$E=Pt=40W\cdot200\cdot4h=32kWh$

$32kWh\cdot14\ \frac{snt}{kWh}=4{,}48€$

7-3
a)
b)
c)

7-4
P=RI^2
U=RI
lamppu a
$I=\frac{U}{R}=\frac{4{,}5}{4}=1{,}125A$
$P=4\cdot1{,}125^2=5{,}0625W$
lamppu b
$I=\frac{U}{R}=\frac{4{,}5V}{6{,}0\Omega}=0{,}75A$
$P=6\cdot0{,}75^2=3{,}375W$
lamppu c
$I=\frac{U}{R}=\frac{9{,}0V}{1{,}5\Omega}=6A$
$P=RI^2=1{,}5\Omega\cdot6A=9W$
lamppu d
$I=\frac{U}{R}=\frac{9{,}0V}{7\Omega}=1{,}2857...A$
$P=RI^2=7\cdot I^2=11{,}5714...W$
lamppu d on kirkkain

7-6
$21h\cdot1{,}5W\cdot365=11497{,}5Wh=11{,}4975kWh$
$11{,}4975\cdot0{,}14\ \frac{€}{kWh}=1{,}60965\approx1{,}61€$
7-7