Electrical Theory & Principles Flashcards

Which of the following correctly describes the behavior of an ideal voltage source?

Answer: It maintains constant terminal voltage regardless of load current

An ideal voltage source has zero internal resistance and maintains its rated voltage regardless of the current drawn by the load.

The phase angle (θ) of a series RL circuit with R = 30 Ω and XL = 40 Ω is:

Answer: 53.13°

θ = arctan(XL/R) = arctan(40/30) = arctan(1.333) ≈ 53.13°, indicating current lags voltage by 53.13°.

Eddy currents in transformer cores are minimized by:

Answer: Laminating the core with thin insulated sheets

Laminated cores break the eddy current paths into smaller, higher-resistance loops, reducing eddy current losses proportional to lamination thickness squared.

The Q factor (quality factor) of a series resonant circuit is defined as:

Answer: Q = XL / R

The Q factor = XL/R (or XC/R) at resonance, representing the ratio of energy stored to energy dissipated per cycle.

In the maximum power transfer theorem, maximum power is delivered to the load when:

Answer: Load resistance equals the source resistance

Maximum power transfer occurs when R_load = R_source (or Z_load = Z_source* for AC circuits), delivering 50% of source power to the load.

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

Answer: 3.77 Ω

XL = 2πfL = 2π × 60 × 0.010 = 3.77 Ω; inductive reactance is directly proportional to frequency and inductance.

Which of the following describes the behavior of a capacitor in a DC steady-state circuit?

Answer: It acts as an open circuit

In DC steady state, no current flows through a fully charged capacitor, making it equivalent to an open circuit.