Electrical Circuits Flashcards

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

Answer: 4

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

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

Answer: 1728 W

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

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

Answer: Maximum power transfer theorem

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

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

Answer: 0.005 s

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

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

Answer: 120 V

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

The mesh current method is most efficiently applied when:

Answer: The circuit has many nodes but few loops

Mesh analysis is preferred when the number of meshes (loops) is less than the number of nodes minus one, reducing the number of equations needed.

What is the impedance of a 10 mH inductor at a frequency of 60 Hz?

Answer: 3.77 Ω

X_L = 2πfL = 2π(60)(0.010) = 3.77 Ω; impedance Z = j3.77 Ω, with magnitude 3.77 Ω.