Electrical Theory & Principles Flashcards

Which of the following best describes impedance in an AC circuit?

Answer: The total opposition to AC current flow combining resistance and reactance

Impedance (Z) is the complex combination of resistance (R) and reactance (X), expressed in ohms: Z = √(R² + X²).

In a three-phase balanced system, the phase voltage is related to the line voltage by:

Answer: V_line = V_phase × √3

In a balanced three-phase wye (star) system, the line voltage equals the phase voltage multiplied by √3 (≈1.732).

The energy stored in a capacitor is expressed as:

Answer: E = ½CV²

The energy stored in a capacitor is E = ½CV², where C is capacitance in farads and V is voltage in volts.

What happens to the total capacitance when capacitors are connected in series?

Answer: Total capacitance decreases below the smallest value

Series capacitors follow the reciprocal rule (1/CT = 1/C1 + 1/C2 + ...), resulting in a total less than the smallest capacitor.

In an AC circuit, resonance occurs when:

Answer: Inductive reactance equals capacitive reactance

Resonance occurs when XL = XC, causing them to cancel, leaving only resistance to limit current, and power factor reaches unity.

The unit of magnetic flux density is the:

Answer: Tesla (T)

Magnetic flux density (B) is measured in Tesla (T), where 1 T = 1 Wb/m², representing flux per unit area.

Which theorem allows a complex linear circuit to be replaced by a single voltage source and series resistance?

Answer: Thevenin's Theorem

Thevenin's Theorem simplifies any linear network to an equivalent voltage source (V_th) in series with a resistance (R_th).