Question

giúp mình vs mình cần gấp

Answer 1

a, khi K mở \(=>\left(R1ntR2\right)\)\(nt\left(R4//R5\right)\)

A2 chỉ 0,5 A\(=>I4=I\left(A2\right)=0,5A=>U4=U5=I4.R4=0,5.80\)\(=40V\)

\(=>I5=\dfrac{U5}{R5}=\dfrac{40}{20}=2A=>I45=I4+I5=2+0,5=2,5A\)\(=Im=I12\)=>số chỉ ampe kế(A1)=2,5A

\(=>R12=R1+R2=4+4=8\left(Om\right)\)

\(=>U12=I12.R12=8.2,5=20V\)\(=>UAB=U12+U4=60V\)

b,khi đóng K\(=>R1nt\left\{[R2nt\left(R4//R5\right)]//R3\right\}\)

\(=>R245=R2+\dfrac{R4.R5}{R4+R5}=4+\dfrac{80.20}{80+20}=20\left(om\right)\)

\(=>R2345=\dfrac{R3.R245}{R3+R345}=\dfrac{5.20}{5+20}=4\left(om\right)\)

\(=>Rtd=R1+R2345=4+4=8\left(om\right)\)

\(=>Im=\dfrac{UAB}{Rtd}=\dfrac{60}{8}=7,5A=I1=I2345\)

\(=>A1\) chỉ 7,5 A

\(=>U2345=I2345.R2345=7,5.4=30V\)\(=U245=U3\)

\(=>I245=\dfrac{U245}{R245}=\dfrac{30}{20}=1,5A=I45\)

\(=>U45=I45.R45=16.1,5=24V=U4\)

\(=>I4=\dfrac{U4}{R4}=\dfrac{24}{80}=0,3A\)\(=>A2\) chỉ 0,3A