The first EMF is 30 V, the second 5V. The resistance of the second resistor is 10 ohms

The first EMF is 30 V, the second 5V. The resistance of the second resistor is 10 ohms, the third is 20 ohms. A current of 1 A flows through the ammeter from top to bottom. Find the resistance of the first resistor. Disregard the resistance of the ammeter and sources.

Given:

E1 = 30 B;

E2 = 5 B;

R2 = 10 Ohm;

R3 = 20 ohms;

I = 1 A.

neglect the resistance of the ammeter and sources.

Find:

R1 -?

Electromotive force is a physical quantity that characterizes the actions of external forces.

Find

E = E1 – E2 = 30V – 5V = 25V.

Let’s calculate the resistance in section 2 – 3:

R2.3 = 10 Ohm + 20 Ohm = 30 Ohm.

From the formula:

I = E / R, let’s express the resistance:

R = E / I.

Insofar as

R = (R1 * R2,3) / (R1 + R2,3), then

30R1 / (30 + R1) = 25.

Let us express from the formula R1:

30 * R1 = 75 + 25 * R1;

5R1 = 75;

R1 = 15 ohms.