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Circuit Theory and Calculations Flashcards

6 cards from real 309A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Circuit Theory and Calculations flashcards as text

  1. What is the inductive reactance of a 50 mH inductor at 60 Hz?

    Answer: 18.85 Ω

    Inductive reactance XL = 2πfL = 2 × 3.14159 × 60 × 0.05 = 18.85 Ω. Reactance increases with both frequency and inductance.

  2. A 120 V circuit has a load that draws 10 A. What is the power dissipated if the power factor is 0.9?

    Answer: 1080 W

    Real power P = V × I × PF = 120 × 10 × 0.9 = 1080 W. The power factor accounts for the phase difference between voltage and current.

  3. In a wye-connected three-phase system, what is the relationship between line voltage and phase voltage?

    Answer: VL = VP × √3

    In a wye (star) connection, the line voltage is √3 times the phase voltage: VL = √3 × VP. Line current equals phase current in a wye connection.

  4. What is the capacitive reactance of a 50 µF capacitor at 60 Hz?

    Answer: 53.05 Ω

    Capacitive reactance XC = 1/(2πfC) = 1/(2 × 3.14159 × 60 × 0.00005) = 1/0.01885 = 53.05 Ω.

  5. A conductor has a resistance of 2 Ω at 20°C. If its temperature rises to 75°C and the temperature coefficient is 0.00393/°C, what is the new resistance?

    Answer: 2.43 Ω

    R2 = R1 × [1 + α(T2 - T1)] = 2 × [1 + 0.00393(75 - 20)] = 2 × [1 + 0.216] = 2 × 1.216 = 2.43 Ω.

  6. What is the efficiency of a motor that outputs 7.5 HP while consuming 6500 W from the supply?

    Answer: 86.1%

    First convert HP to watts: 7.5 × 746 = 5595 W. Efficiency = (Output/Input) × 100 = (5595/6500) × 100 = 86.1%.