ISCET AC Circuits and Analysis Questions and Answers

Question 1

In a series RLC circuit, what is the condition known as resonance?

Accepted Answer

The total impedance is equal to the resistance.

Answer

Resonance in a series RLC circuit occurs at the specific frequency where the inductive reactance (XL) equals the capacitive reactance (XC). When XL = XC, they cancel each other out in the impedance formula Z = √(R² + (XL - XC)²). This simplifies the impedance to Z = √R², meaning the total impedance (Z) is equal to the resistance (R), and the circuit behaves as purely resistive. At this point, the current in the circuit reaches its maximum value.

Question 2

A technician is analyzing an AC circuit and notes that the current waveform leads the voltage waveform. Which of the following best describes the load?

Accepted Answer

Primarily capacitive

Answer

In an AC circuit, the phase relationship between current and voltage depends on the type of load. For a capacitive load, the current leads the voltage. Conversely, for an inductive load, the current lags the voltage. In a purely resistive circuit, the current and voltage are in phase.

Question 3

What is the primary purpose of improving the power factor in an AC circuit, ideally towards unity (1.0)?

Accepted Answer

To reduce the total current drawn from the source for the same amount of real power.

Answer

Power factor is the ratio of real power (used to do work) to apparent power (total power supplied). A low power factor indicates that a significant portion of the current is not performing useful work. By improving the power factor towards unity (1.0), the apparent power becomes nearly equal to the real power. This means less total current is required from the source to deliver the same amount of real power, which reduces energy losses in the distribution system and allows for more efficient operation.

Question 4

A series AC circuit consists of a 30 Ω resistor and a capacitor with a capacitive reactance (XC) of 40 Ω. What is the total impedance (Z) of this circuit?

Accepted Answer

50 Ω

Answer

For a series RC circuit, the total impedance (Z) is calculated using the formula Z = √(R² + XC²). In this case, R = 30 Ω and XC = 40 Ω. So, Z = √(30² + 40²) = √(900 + 1600) = √2500 = 50 Ω. Impedance represents the total opposition to current flow in an AC circuit.

Question 5

Which of the following will cause the resonant frequency of a series LC circuit to decrease?

Accepted Answer

Increasing the capacitance.

Answer

The formula for resonant frequency (f₀) in an LC circuit is f₀ = 1 / (2π√(LC)). This formula shows that the resonant frequency is inversely proportional to the square root of both the inductance (L) and the capacitance (C). Therefore, increasing either the capacitance or the inductance will cause the resonant frequency to decrease.

(ISCET) International Society of Certified Electronics Technicians Practice Test

(ISCET) International Society of Certified Electronics Technicians Practice Test

ISCET AC Circuits and Analysis Questions and Answers