Δt=20 min=1200 s
a) 1/R₂₃=1/R₂+1/R₃=>R₂₃=R₂R₃/(R₂+R₃)=6*3/(6+3)=18/9=2 Ω
b) Re=R₁+R₂₃=7+2=9 Ω
c) I=I₂+I₃
E=I(R₁+r)+I₂R₂
E=I(R₁+r)+I₃R₃
0=I₃R₃-I₂R₂
d) 0=I₃R₃-I₂R₂<=>I₂R₂=I₃R₃<=>6I₂=3I₃ |:3=>2I₂=I₃
I=I₂+I₃<=>I=I₂+2I₂=3I₂=>I₂=I/3=1,2/3=0,4 A
e) I=E/(Re+r)<=>IRe+Ir=E<=>1,2*9+1,2r=12<=>1,2r=1,2=>r=1 Ω
f) U₂=I₂R₂=0,4*6=2,4 V
g) P=EI=12*1,2=14,4 W
h) W₂=U₂I₂Δt=2,4*0,4*1200=1152 J
g) η=Re/(Re+r)=9/(9+1)=9/10=0,9=90%
