Question

How do I calculate the resistence of R2 current, which is parallel to R1 (resistence 4 ohm, current 2,25 A). Additional to that I have a resistence R3 which is a series circuit (5 ohm) next to the R1 and R2. They are all on a 24 V battery.

Answer 1

Current through resistance R3:

Voltage on R1:

$U_1=I_1R_1$

Since R1 and R2 are parallel, then:

$U_1=U_2=I_2R_2$

Total voltage:

$U=U_1+U_3=I_1R_1+I_3R_3$

Then:

$I_3=\frac{U-I_1R_1}{R_3}=\frac{24-2.25\cdot4}{5}=3A$

$I_2=I_3-I_1=3-2.25=0.75A$

$R_2=\frac{I_1R_1}{I_2}=\frac{2.25\cdot4}{0.75}=12$ ohm