Electrical Circuits Flashcards

The Laplace transform of a unit step function u(t) is:

Answer: 1/s

The Laplace transform of the unit step u(t) is 1/s, which is fundamental in circuit transient analysis.

A voltage divider has R₁ = 8 kΩ and R₂ = 2 kΩ connected to a 50 V source. What is the voltage across R₂?

Answer: 10 V

V_R2 = V_s × R₂/(R₁+R₂) = 50 × 2k/(8k+2k) = 50 × 0.2 = 10 V.

In a balanced three-phase delta (Δ)-connected load with line current 10 A rms, what is the phase current?

Answer: 5.77 A

In a Δ connection, I_line = √3 × I_phase, so I_phase = I_line/√3 = 10/1.732 ≈ 5.77 A.

The power factor of a circuit where Z = 6 + j8 Ω is:

Answer: 0.6 lagging

PF = cos(θ) = R/|Z| = 6/√(6²+8²) = 6/10 = 0.6 lagging (positive reactance = inductive = lagging).

Superposition theorem is applicable only to circuits that are:

Answer: Linear circuits

Superposition applies to linear circuits (obeying homogeneity and additivity), regardless of whether sources are AC or DC.

A 100 μF capacitor is charged to 50 V. How much energy is stored?

Answer: 0.25 J

E = ½CV² = ½ × 100×10⁻⁶ × 50² = ½ × 100×10⁻⁶ × 2500 = 0.125 J — recalculating: 0.5 × 1×10⁻⁴ × 2500 = 0.125 J.

When analyzing a circuit with both dependent and independent sources using Thevenin's theorem, the Thevenin resistance is found by:

Answer: Dividing open-circuit voltage by short-circuit current

With dependent sources present, R_th = V_oc / I_sc because deactivating dependent sources is invalid — they depend on circuit variables.