NECA Electrical Theory & Principles 2 — Questions and Answers
Question 1: What happens to the total resistance when resistors are connected in parallel?
- It equals the sum of all resistors
- It is always less than the smallest resistor (Correct answer)
- It equals the largest resistor value
- It doubles with each added resistor
Correct answer: It is always less than the smallest resistor
In a parallel circuit, the total resistance is always less than the smallest individual resistor because current has multiple paths to flow through.
Question 2: Which law states that the algebraic sum of all currents entering and leaving a node equals zero?
- Ohm's Law
- Faraday's Law
- Kirchhoff's Current Law (Correct answer)
- Lenz's Law
Correct answer: Kirchhoff's Current Law
Kirchhoff's Current Law (KCL) states that the sum of currents entering a junction equals the sum of currents leaving it, based on conservation of charge.
Question 3: A capacitor in a DC circuit, after fully charging, acts as:
- A short circuit
- An open circuit (Correct answer)
- A resistor
- An inductor
Correct answer: An open circuit
Once fully charged, a capacitor blocks DC current because no more current flows when the capacitor voltage equals the source voltage, effectively acting as an open circuit.
Question 4: What is the unit of magnetic flux density?
- Weber
- Tesla (Correct answer)
- Henry
- Gauss only
Correct answer: Tesla
Tesla (T) is the SI unit of magnetic flux density, defined as one weber per square meter (Wb/m²).
Question 5: In an AC circuit, when voltage and current are in phase, the power factor is:
- 0
- 0.5
- 1 (Correct answer)
- Negative
Correct answer: 1
A power factor of 1 (unity) occurs when voltage and current are perfectly in phase, meaning all power delivered is real (active) power with no reactive component.
Question 6: The phenomenon where a changing magnetic field induces a voltage in a conductor is called:
- Piezoelectric effect
- Electromagnetic induction (Correct answer)
- Thermoelectric effect
- Photoelectric effect
Correct answer: Electromagnetic induction
Electromagnetic induction, discovered by Michael Faraday, is the production of an EMF (and thus a current) in a conductor exposed to a changing magnetic flux.
Question 7: What is the reactance of a 10 mH inductor at 60 Hz?
- 3.77 Ω (Correct answer)
- 6.28 Ω
- 0.6 Ω
- 37.7 Ω
Correct answer: 3.77 Ω
Inductive reactance XL = 2πfL = 2π × 60 × 0.010 = 3.77 Ω.
NECA Electrical Theory & Principles 2
What happens to the total resistance when resistors are connected in parallel?