Bài 13:
a. \(R=R1+\left(\dfrac{R2\cdot R3}{R2+R3}\right)=18+\left(\dfrac{30\cdot20}{30+20}\right)=30\Omega\)
b. \(I=I1=I23=U:R=15:30=0,5A\left(R1ntR23\right)\)
\(U23=U2=U3=I23\cdot R23=0,5\cdot\left(\dfrac{30\cdot20}{30+20}\right)=6V\left(R2//R3\right)\)
\(\left\{{}\begin{matrix}I2=U2:R2=6:30=0,2A\\I3=U3:R3=6:20=0,3A\end{matrix}\right.\)
Bài 14:
a. \(P=1100\)W
b. \(A=UIt=Pt=1100\cdot3\cdot60=198000\left(J\right)\)
c. \(A'=UIt'=220\left(\dfrac{1100}{220}\right)\cdot\dfrac{45}{60}\cdot30=24750\)Wh = 24,75kWh
\(\Rightarrow T=A'\cdot1500=24,75\cdot1500=37125\left(dong\right)\)
