AC Fundamentals and Phasors - Exam Prep Problem Set

AC Fundamentals and Phasors - Problem Set

Q. According to Kirchhoff's Current Law (KCL), what must be true at any junction in a circuit?

A. The sum of voltages is zero
B. The sum of currents entering equals the sum of currents leaving
C. Power is conserved
D. Current is constant throughout the circuit

Solution

KCL states that the sum of currents entering a junction must equal the sum of currents leaving the junction.

Correct Answer: B — The sum of currents entering equals the sum of currents leaving

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Q. In a circuit with a current of 5 A and a resistance of 10 ohms, what is the voltage across the resistor?

A. 50 V
B. 5 V
C. 10 V
D. 15 V

Solution

Using Ohm's Law, V = I * R = 5 A * 10 ohms = 50 V.

Correct Answer: A — 50 V

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Q. In an AC circuit, if the voltage is given as V(t) = 100√2 sin(ωt), what is the RMS voltage?

A. 100 V
B. 70.71 V
C. 141.42 V
D. 50 V

Solution

The RMS voltage (V_rms) for a sinusoidal waveform is V_peak / √2, so V_rms = 100√2 / √2 = 100 V.

Correct Answer: B — 70.71 V

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Q. What is the equivalent resistance of two resistors in parallel, R1 = 4 ohms and R2 = 6 ohms?

A. 2.4 ohms
B. 10 ohms
C. 24 ohms
D. 1.5 ohms

Solution

The equivalent resistance for resistors in parallel is given by 1/R_eq = 1/R1 + 1/R2, which results in R_eq = 2.4 ohms.

Correct Answer: A — 2.4 ohms

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Q. What is the impedance of a circuit with a resistance of 3 ohms and a reactance of 4 ohms?

A. 5 ohms
B. 7 ohms
C. 12 ohms
D. 1.33 ohms

Solution

Impedance (Z) is calculated using the formula Z = √(R^2 + X^2), so Z = √(3^2 + 4^2) = 5 ohms.

Correct Answer: A — 5 ohms

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Q. What is the Norton equivalent current for a circuit with a 10 ohm resistor across a 20 V source?

A. 2 A
B. 0.5 A
C. 20 A
D. 10 A

Solution

The Norton equivalent current (I_N) is calculated as I_N = V/R = 20 V / 10 ohms = 2 A.

Correct Answer: A — 2 A

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Q. What is the power consumed by a 120 V AC circuit with a current of 10 A?

A. 1200 W
B. 100 W
C. 10 W
D. 120 W

Solution

Power (P) is calculated as P = V * I, so P = 120 V * 10 A = 1200 W.

Correct Answer: A — 1200 W

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Q. What is the Thevenin equivalent voltage across a load resistor in a simple circuit with a 12 V battery and a 4 ohm resistor in series?

A. 12 V
B. 6 V
C. 4 V
D. 0 V

Solution

The Thevenin equivalent voltage is the same as the source voltage, which is 12 V.

Correct Answer: A — 12 V

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Q. What is the Thevenin equivalent voltage if the open-circuit voltage across the terminals is 15V?

A. 0 V
B. 15 V
C. 30 V
D. 45 V

Solution

The Thevenin equivalent voltage is equal to the open-circuit voltage, which is 15 V.

Correct Answer: B — 15 V

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Q. What is the total impedance of a series circuit with a resistor of 4 ohms and an inductor with a reactance of 3 ohms?

A. 7 ohms
B. 1 ohm
C. 12 ohms
D. 8 ohms

Solution

In a series circuit, total impedance Z = R + jX, so Z = 4 + j3, which has a magnitude of 7 ohms.

Correct Answer: A — 7 ohms

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Q. What is the total voltage in a series circuit with a 12V battery and two resistors of 4 ohms and 6 ohms?

A. 12 V
B. 10 V
C. 8 V
D. 6 V

Solution

In a series circuit, the total voltage is equal to the source voltage, which is 12 V.

Correct Answer: A — 12 V

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AC Fundamentals and Phasors - Problem Set

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