CET DC Circuit Analysis & Theory 2 — Questions and Answers
Question 1: Three resistors of 10 Ω, 20 Ω, and 30 Ω are connected in series across a 120 V supply. What is the voltage drop across the 20 Ω resistor?
- 20 V
- 40 V (Correct answer)
- 60 V
- 80 V
Correct answer: 40 V
Total resistance is 60 Ω; current = 2 A; V = 2 A × 20 Ω = 40 V.
Question 2: Which law states that the algebraic sum of all voltages around any closed loop in a circuit equals zero?
- Ohm's Law
- Kirchhoff's Current Law
- Kirchhoff's Voltage Law (Correct answer)
- Norton's Theorem
Correct answer: Kirchhoff's Voltage Law
Kirchhoff's Voltage Law (KVL) states that the sum of EMFs equals the sum of voltage drops around any closed loop.
Question 3: A 60 W lamp operates at 120 V. What is its resistance?
- 120 Ω
- 180 Ω
- 240 Ω (Correct answer)
- 360 Ω
Correct answer: 240 Ω
R = V²/P = 120²/60 = 14400/60 = 240 Ω.
Question 4: In a voltage divider with R1 = 4 kΩ and R2 = 1 kΩ connected to 25 V, what is the output voltage across R2?
- 1 V
- 5 V (Correct answer)
- 20 V
- 25 V
Correct answer: 5 V
Vout = Vin × R2/(R1+R2) = 25 × 1/5 = 5 V.
Question 5: What happens to total resistance when additional resistors are added in series?
- Decreases
- Remains the same
- Increases (Correct answer)
- Becomes zero
Correct answer: Increases
Series resistances add directly, so total resistance always increases with each addition.
Question 6: A circuit has a 9 V battery and a 3 Ω internal resistance with a 6 Ω external load. What current flows through the circuit?
- 0.5 A
- 1 A (Correct answer)
- 1.5 A
- 3 A
Correct answer: 1 A
I = V / (r + R) = 9 / (3 + 6) = 9/9 = 1 A.
Question 7: Power dissipated in a resistor doubles when the current through it is:
- Doubled
- Halved
- Increased by √2 (Correct answer)
- Multiplied by 4
Correct answer: Increased by √2
P = I²R, so to double P, I must increase by √2 since (√2)² = 2.
CET DC Circuit Analysis & Theory 2
Three resistors of 10 Ω, 20 Ω, and 30 Ω are connected in series across a 120 V supply.
What is the voltage drop across the 20 Ω resistor?