NETA - InterNational Electrical Testing Association Certified Technicians AC/DC Theory and Circuits Questions and Answers

Question 1

A technician is analyzing a series AC circuit operating at 60 Hz. The circuit contains a resistor (R) of 8 ohms, an inductor with an inductive reactance (XL) of 10 ohms, and a capacitor with a capacitive reactance (XC) of 4 ohms. What is the total impedance (Z) of this circuit?

Accepted Answer

10.0 ohms

Answer

The total impedance (Z) in a series RLC circuit is calculated using the formula: Z = √[R² + (XL - XC)²]. In this case, Z = √[8² + (10 - 4)²] = √[64 + 6²] = √[64 + 36] = √100 = 10.0 ohms.

Question 2

In an AC power system, which of the following best describes the relationship between true power (P), reactive power (Q), and apparent power (S)?

Accepted Answer

Apparent power is the vector sum of true power and reactive power.

Answer

The relationship between true power (measured in Watts), reactive power (measured in VAR), and apparent power (measured in VA) is represented by the power triangle. Apparent power (S) is the hypotenuse, representing the vector sum of true power (P) and reactive power (Q), expressed by the formula S² = P² + Q².

Question 3

A technician closes a switch to apply a DC voltage source to a circuit containing only a resistor and a large inductor in series. Immediately at the instant the switch is closed (t=0), how does the inductor behave?

Accepted Answer

As an open circuit, with maximum voltage drop.

Answer

Due to its property of opposing a change in current, an inductor will initially behave as an open circuit the moment a DC voltage is applied. At this instant (t=0), current has not yet begun to flow, so the current is zero, and the full source voltage is dropped across the inductor.

Question 4

A field service report notes that a three-phase transformer is consistently running hotter than its nameplate rating would suggest, despite the load current being within limits. Which of the following is the most likely cause for the overheating?

Accepted Answer

High levels of harmonic distortion

Answer

Harmonic currents, which are multiples of the fundamental frequency, can cause significant additional heating in the windings and core of a transformer due to increased eddy current and hysteresis losses. This leads to overheating even when the fundamental load current is not excessive.

Question 5

A technician uses a power quality analyzer on an AC circuit and measures the true power as 4.0 kW and the apparent power as 5.0 kVA. What is the power factor of this circuit?

Accepted Answer

0.80

Answer

Power factor (PF) is defined as the ratio of true power (P) to apparent power (S). The formula is PF = P / S. In this scenario, PF = 4.0 kW / 5.0 kVA = 0.80.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA - InterNational Electrical Testing Association Certified Technicians AC/DC Theory and Circuits Questions and Answers