Electrical Principles and Units Flashcards

What is the capacitive reactance of a 100 pF capacitor at 10 MHz?

Answer: 159 Ω

Xc = 1/(2πfC) = 1/(2π × 10⁷ × 10⁻¹⁰) ≈ 159 Ω.

A coil has inductive reactance of 100 Ω at 1 MHz. What is its inductance?

Answer: 15.9 μH

L = XL/(2πf) = 100/(2π × 10⁶) ≈ 15.9 μH.

Two 10 μF capacitors are connected in series. What is the total capacitance?

Answer: 5 μF

For two equal capacitors in series, Cs = C/2 = 10/2 = 5 μF.

Two inductors of 100 μH and 200 μH are connected in series with no mutual coupling. What is the total inductance?

Answer: 300 μH

Series inductors (no mutual coupling) add directly: 100 + 200 = 300 μH.

What happens to capacitive reactance as frequency increases?

Answer: It decreases

Since Xc = 1/(2πfC), reactance is inversely proportional to frequency and decreases as frequency rises.

What is the energy stored in a 10 μF capacitor charged to 100 V?

Answer: 50 mJ

E = ½CV² = ½ × 10×10⁻⁶ × 100² = 0.05 J = 50 mJ.

Two capacitors of 20 μF and 30 μF are connected in parallel. What is the total capacitance?

Answer: 50 μF

Capacitors in parallel add directly: 20 + 30 = 50 μF.