[tex]R_{1,2}=\frac{R1R_2}{R_1+R_2}=\frac{6*2}{6+2}=\frac{12}{8}= 1,5\Omega \\R_e=R_{1,2}+R_3+R_4=1,5+4+1=6,5\Omega\\I=\frac{E}{R_e+r}=\frac{14}{6,5+1,5}=\frac{14}{8}=1,75A\\ E=I(r+R_4+R_3)+I_1R_2<=>14=I(0,5+4+1)+6I_1<=>14=5,5I+6I_1(1)\\E=I(r+R_4+R_3)+I_2R_1<=>14=I(0,5+4+1)+2I_2<=>14=5,5I+2I_2(2)\\(1)-(2)=>6I_1-2I_2=0=>I_2=3I_1\\ I=I_1+I_2=I_1+3I_1=4I_1=>I_1=\frac{I}{4}=\frac{1,75}{4}=0,43A \\I_2=3I_1=3*0,43=1,31 A[/tex]
[tex]t=10 min=600 s\\W=R_3I^2t=1*1,75^2*600=1837,5J\\P=EI=14*1,75=24,5W\\\eta=\frac{R_e}{R_e+r}=\frac{6,5}{6,5+0,5}=\frac{6,5}{7}= 0,928=>\eta=92,8\%[/tex]
