NEIEP 600 Final Exam Practice Test – 100 Questions with Rationales

In capacitors, what is the purpose of the dielectric? A. To increase capacitance B. To prevent arcing within the capacitor C. To reduce resistance D. To store electrons Correct Answer: B. To prevent arcing within the capacitor Explanation: The dielectric is an insulating material between capacitor plates that prevents arcing (current jumping between plates) while allowing electrostatic charge storage. --- Question 2 Which of the following is true about capacitors in AC circuits? A. Voltage leads current B. Current leads voltage all the time C. Current and voltage are in phase D. Current lags voltage Correct Answer: B. Current leads voltage all the time Explanation: In a purely capacitive AC circuit, current leads voltage by 90 degrees. This is opposite of an inductive circuit where current lags voltage. --- Question 3 What describes a capacitor’s ability to store an electrical charge? A. Resistance B. Inductance C. Capacitance D. Impedance Correct Answer: C. Capacitance Explanation: Capacitance (measured in farads) is the ability of a capacitor to store an electrical charge. It is determined by plate area, distance between plates, and dielectric material. --- Question 4 Which of the following statements is correct about polarized electrolytic capacitors? A. Voltage polarity does not matter B. Voltage polarity must be correct C. They can be used in AC circuits only D. They have no dielectric Correct Answer: B. Voltage polarity must be correct Explanation: Polarized electrolytic capacitors have a positive and negative terminal. Reverse polarity can cause dielectric breakdown, overheating, and explosion. --- Question 5 What is the time constant for a circuit with 150k ohms and 2 microfarad capacitor? A. 0.3 seconds B. 0.03 seconds C. 3.0 seconds D. 300 seconds Correct Answer: A. 0.3 seconds Explanation: Time constant (τ) = R × C = 150,000 Ω × 0.000002 F = 0.3 seconds. --- Question 6 If frequency is increased in a capacitive circuit, what will happen to capacitive reactance? A. Capacitive reactance will increase B. Capacitive reactance will decrease C. Capacitive reactance will stay the same D. Capacitive reactance will become zero Correct Answer: B. Capacitive reactance will decrease Explanation: Capacitive reactance (Xc = 1/(2πfC)) is inversely proportional to frequency. As frequency increases, Xc decreases. --- Question 7 What happens in a DC circuit when the capacitor voltage equals the source voltage? A. Current flow stops in the circuit B. Current flow is maximum C. The capacitor is shorted D. The capacitor discharges Correct Answer: A. Current flow stops in the circuit Explanation: When fully charged, capacitor voltage equals source voltage, no potential difference exists, so current flow stops (open circuit condition). --- Question 8 In a DC circuit, which is correct about capacitors the instant when power is applied? A. Current is zero B. Current is maximum C. Voltage is maximum D. The capacitor is fully charged Correct Answer: B. Current is maximum Explanation: At the instant power is applied, the capacitor acts as a short circuit (zero voltage, maximum current). Current then decreases exponentially as the capacitor charges. --- Question 9 What is the total capacitance of three capacitors (100 µF, 100 µF, 50 µF) connected in parallel? A. 25 µF B. 150 µF C. 250 µF D. 500 µF Correct Answer: C. 250 µF Explanation: Capacitors in parallel add: Ctotal = 100 + 100 + 50 = 250 µF. --- Question 10 If a circuit has a capacitor of 5 microfarads and a source voltage of 120 volts DC through a resistance of 200k ohms, how long will it take to fully charge? A. 0.5 seconds B. 1 second C. 5 seconds D. 10 seconds Correct Answer: C. 5 seconds Explanation: A capacitor is considered fully charged after 5 time constants. τ = R × C = 200,000 × 0.000005 = 1 second. 5τ = 5 × 1 = 5 seconds.