Step-by-Step Guide: Calculating Current & Voltage Across R2 in Electrical Circuits (Image Included)

sebastiane94 wrote:

1. Calculate the equivalent resistance "Rz23" for R2 and R3
2. Calculate the equivalent resistance "Rz" for R1 and Rz23
3. Calculate the total current flowing in the circuit from Ohm's law. You use the formula I = E / (Rz + Rw).
4. Calculate the voltage across the resistors using the formula U = R * I. The voltage across R2 is equal to the difference of the emf with the sum of the potential drops across Rw and R1 (UR2 = E - (UR1 + URw).
5. The current through IR2 and IR3 is not equal to IR1!! It should be calculated from the voltage that prevails on these resistances (from the relationship of voltages in parallel connection).

Ad.1
1/Rz23 = 1/3 + 1/6 = 2/6 + 1/6 = 3/6
Rz23 = 6/3 = 2 ohms

Ad.2
Rz = 1.5 + 2 = 3.5 ohms

Ad.3
I = 12 / (3.5 + 0.5) = 12/4 = 3A

Ad.4
U = R * I
URw = 0.5 * 3 = 1.5V
UR1 = 1.5 * 3 = 4.5V
UR2 = UR3 = 12 - (1.5+4.5) = 6V

Ad.5
I = U / R
IR2=6/3=2A
IR3 = 6 / 6 = 1A