NCEES Electrical Circuits 3

Question 1

Using the node voltage method, how many independent equations are needed for a circuit with 5 nodes (including the reference node)?

Accepted Answer

4

Answer

The node voltage method requires (N − 1) equations for N nodes, so 5 nodes yield 4 independent node equations.

Question 2

A 120 V rms source delivers power to a load with impedance Z = 3 + j4 Ω. What is the real power consumed?

Accepted Answer

1728 W

Answer

I_rms = 120/|Z| = 120/5 = 24 A; P = I²R = (24)²×3 = 576×3 = 1728 W.

Question 3

Which theorem states that maximum power is transferred to a load when the load impedance equals the complex conjugate of the source impedance?

Accepted Answer

Maximum power transfer theorem

Answer

The Maximum Power Transfer Theorem states Z_L = Z_S* (complex conjugate) for maximum power delivery in AC circuits.

Question 4

The time constant of an RL circuit with R = 50 Ω and L = 0.25 H is:

Accepted Answer

0.005 s

Answer

Time constant τ = L/R = 0.25/50 = 0.005 s (5 ms).

Question 5

In a balanced three-phase Y-connected system, if the line voltage is 208 V rms, the phase voltage is approximately:

Accepted Answer

120 V

Answer

For a Y-connected system, V_phase = V_line/√3 = 208/1.732 ≈ 120 V rms.

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