Question

How to determine the voltage Ub2 so that the current through R2 would be equal to 0,150A using Kirchoff's Law? Thank you!

I've drawn the arrows already. I hope they're right. But now I don't know which equations to make?

If it's blurry, here's the given data:
Ub1 = 20V
Ub2 = unknown
R1 = 300 Ohm
R2 = 100 Ohm
R3 = 200 Ohm

Answer 1

From the directions you have made,we can say, `I_3=I_1 + I_2`

Now,volatge drop across the three wires will be the same,as no battery or resistance is intervening in between them.Let this be `V_a -V_b`

Now,given, `I_2 = 0.150A`

So,voltage drop across `100 ohm` is `100×0.150=15 V=V_a-V_b`

So,using Kirchoff's law for the upper wire,we get, `V_a-V_b = +20 -I_1×300=15` or, `I_1=0.017 A`

So, current flowing through `200 ohm` is `I_1+I_2=(0.017+0.150)=0.167A`

So,using Kirchoff's law,for the lower wire,

`V_a - V_b = -Ub_2 +200×0.167=15`

Or, `Ub_2 = 18.4 V`