If the EMF and the internal resistance of one battery element in the above circuit are 2.5 V and 1.5 Ohm

If the EMF and the internal resistance of one battery element in the above circuit are 2.5 V and 1.5 Ohm, R1 = 5 Ohm, respectively, and the current through this resistance is 0.85 A, then what will be the resistance R2.

Given:
EMF1 = 2.5 V;
EMF2 = 1.5 V;
R1 = 5 ohms;
J1 = 0.85 A.
Find: R2.
Decision:
1) First you need to find the total EMF. To do this, you need to multiply EMF1 by three.
Total EMF = 3 * 2.5 = 7.5 V.
2) Next, you need to find the voltage. We need the voltage that will be across the resistor R1. Let’s write down the formula for finding:
U1 = J1 * R1
Let’s substitute the values ​​into it:
U1 = 0.85 * 5 = 4.25 V.
3) Find the voltage drop across the batteries. To do this, subtract the voltage U1 across the resistor R1 from the total EMF.
u = 7.5 – 4.25 = 3.25 B.
4) Find the current. For this we use the following formula: J = u / EMF2.
Substitute the values:
J = 3.25 / 1.5 ≈ 2 A.
5) Next, you need to find the current through the second resistor using the formula:
J2 = 2 – 0.85 = 1.25 A
6) Now we can find the resistance across the second resistor.
We use the formula: R2 = U1 / J2.
Substitute the values ​​we already know and find the answer.
R2 = 4.25 / 1.25 = 3.4 ohm
Answer: 3.4