In a series circuit with resistors 2 Ω, 4 Ω, and 6 Ω and a 24 V source, what is the current? What is the voltage across the 4 Ω resistor?

• A. Total R = 8 Ω; I = 3 A; V4Ω = 12 V
• B. Total R = 4 Ω; I = 6 A; V4Ω = 24 V
• C. Total R = 24 Ω; I = 1 A; V4Ω = 4 V
• D. Total R = 12 Ω; I = 2 A; V4Ω = 8 V

Answer: (D)

In a series circuit the current is the same through every resistor and the resistances add together to give the total resistance. Add them: 2 Ω + 4 Ω + 6 Ω = 12 Ω. The current is then I = V / R_total = 24 V / 12 Ω = 2 A. The voltage across the 4 Ω resistor is V = I × R = 2 A × 4 Ω = 8 V. So the total resistance is 12 Ω, the current is 2 A, and the voltage across the 4 Ω resistor is 8 V.