IST Electrical and Electronic Knowledge 2 — Questions and Answers
Question 1: What does AC stand for in electrical systems?
- Alternating Circuit
- Alternating Current (Correct answer)
- Amplified Current
- Automatic Control
Correct answer: Alternating Current
AC stands for Alternating Current, which periodically reverses direction, unlike Direct Current (DC).
Question 2: What is the standard frequency of AC power in the United States?
- 50 Hz
- 60 Hz (Correct answer)
- 120 Hz
- 240 Hz
Correct answer: 60 Hz
The US power grid operates at 60 Hz, meaning the current alternates direction 60 times per second.
Question 3: What is the function of a transformer in an electrical system?
- Convert AC to DC power
- Change voltage levels from one level to another (Correct answer)
- Measure electrical current flow
- Regulate frequency of the power supply
Correct answer: Change voltage levels from one level to another
Transformers step AC voltage up or down to different levels using electromagnetic induction.
Question 4: A motor nameplate shows 480V/3-phase. What does '3-phase' indicate?
- The motor has three speed settings
- The motor uses three separate AC waveforms offset by 120 degrees (Correct answer)
- The motor requires three separate ground wires
- The motor operates at three distinct power levels
Correct answer: The motor uses three separate AC waveforms offset by 120 degrees
Three-phase power uses three AC waveforms that are each offset by 120 degrees, providing more efficient power delivery for industrial motors.
Question 5: If two 10-Ohm resistors are connected in parallel, what is the total resistance?
- 5 Ohms (Correct answer)
- 10 Ohms
- 20 Ohms
- 0.1 Ohms
Correct answer: 5 Ohms
For two equal resistors in parallel, total resistance = R/2 = 10/2 = 5 Ohms.
Question 6: What instrument is used to measure electrical voltage?
- Ammeter
- Ohmmeter
- Voltmeter (Correct answer)
- Wattmeter
Correct answer: Voltmeter
A voltmeter measures the electrical potential difference (voltage) between two points in a circuit.
IST Electrical and Electronic Knowledge 2
What does AC stand for in electrical systems?