GROL Electrical Principles and Units 3 — Questions and Answers
Question 1: What is the capacitive reactance of a 100 pF capacitor at 10 MHz?
- 15.9 Ω
- 159 Ω (Correct answer)
- 1590 Ω
- 15,900 Ω
Correct answer: 159 Ω
Xc = 1/(2πfC) = 1/(2π × 10⁷ × 10⁻¹⁰) ≈ 159 Ω.
Question 2: A coil has inductive reactance of 100 Ω at 1 MHz. What is its inductance?
- 0.159 μH
- 1.59 μH
- 15.9 μH (Correct answer)
- 159 μH
Correct answer: 15.9 μH
L = XL/(2πf) = 100/(2π × 10⁶) ≈ 15.9 μH.
Question 3: Two 10 μF capacitors are connected in series. What is the total capacitance?
- 5 μF (Correct answer)
- 10 μF
- 20 μF
- 100 μF
Correct answer: 5 μF
For two equal capacitors in series, Cs = C/2 = 10/2 = 5 μF.
Question 4: Two inductors of 100 μH and 200 μH are connected in series with no mutual coupling. What is the total inductance?
- 66.7 μH
- 150 μH
- 200 μH
- 300 μH (Correct answer)
Correct answer: 300 μH
Series inductors (no mutual coupling) add directly: 100 + 200 = 300 μH.
Question 5: What happens to capacitive reactance as frequency increases?
- It increases proportionally
- It remains constant
- It decreases (Correct answer)
- It increases exponentially
Correct answer: It decreases
Since Xc = 1/(2πfC), reactance is inversely proportional to frequency and decreases as frequency rises.
Question 6: What is the energy stored in a 10 μF capacitor charged to 100 V?
- 1 mJ
- 5 mJ
- 50 mJ (Correct answer)
- 500 mJ
Correct answer: 50 mJ
E = ½CV² = ½ × 10×10⁻⁶ × 100² = 0.05 J = 50 mJ.
Question 7: Two capacitors of 20 μF and 30 μF are connected in parallel. What is the total capacitance?
- 12 μF
- 25 μF
- 50 μF (Correct answer)
- 600 μF
Correct answer: 50 μF
Capacitors in parallel add directly: 20 + 30 = 50 μF.
GROL Electrical Principles and Units 3
What is the capacitive reactance of a 100 pF capacitor at 10 MHz?