NCEES Electrical Circuits 4

Question 1

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

Accepted Answer

1/s

Answer

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

Question 2

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

Accepted Answer

10 V

Answer

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

Question 3

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

Accepted Answer

5.77 A

Answer

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

Question 4

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

Accepted Answer

0.6 lagging

Answer

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

Question 5

Superposition theorem is applicable only to circuits that are:

Accepted Answer

Linear circuits

Answer

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

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