Câu 9:
a, $R_{tđ}=\dfrac{R_{1}.R_{2}}{R_{1}+R_{2}}$
$=\dfrac{15.10}{15+10}=6$ Ω
b, $P=\dfrac{U^2}{R_{tđ}}=\dfrac{U^2}{R_{tđ}}=\dfrac{12^2}{6}=24W$
Điện năng tiêu thụ trong $10p=\dfrac{1}{6}h$: $A=P.t=24.\dfrac{1}{6}=4Wh$
Câu 10:
a, $Q_{i}=m.c.Δt$
$=3.4200.(100-20)$
$=1008000J$
b, $Q_{tp}=Q_{i}:H$
$=1008000:80\%$
$=1260000J$
$=1260kJ$