CPT Electrical & Mechanical Fundamentals 2 — Questions and Answers
Question 1: A motor nameplate reads 460V, 3-phase. What happens if this motor is connected to 230V, 3-phase?
- Motor runs at double speed
- Motor draws excessive current and overheats (Correct answer)
- Motor runs normally at half power
- Motor runs cooler than rated
Correct answer: Motor draws excessive current and overheats
Running a motor at half its rated voltage causes it to draw excessive current to maintain torque, leading to overheating and potential burnout.
Question 2: Which type of bearing is best suited for applications with high radial loads and moderate axial loads?
- Thrust bearing
- Deep groove ball bearing
- Needle bearing
- Tapered roller bearing (Correct answer)
Correct answer: Tapered roller bearing
Tapered roller bearings are designed to handle both high radial loads and significant axial (thrust) loads simultaneously.
Question 3: What does the term 'power factor' describe in an AC electrical circuit?
- The ratio of real power to apparent power (Correct answer)
- The ratio of voltage to current
- The efficiency of a transformer
- The frequency of the AC supply
Correct answer: The ratio of real power to apparent power
Power factor is the ratio of real (useful) power in watts to apparent power in volt-amperes, indicating how efficiently electrical power is being used.
Question 4: In a V-belt drive system, what is the consequence of excessive belt tension?
- Reduced belt slip
- Premature bearing failure and belt wear (Correct answer)
- Increased power transmission efficiency
- Improved speed control
Correct answer: Premature bearing failure and belt wear
Excessive belt tension places extreme radial loads on shaft bearings, accelerating bearing wear while also shortening belt life.
Question 5: A single-phase 120V circuit has a resistance of 12 ohms. What is the current flow?
- 1,440 A
- 10 A (Correct answer)
- 132 A
- 0.1 A
Correct answer: 10 A
Using Ohm's Law: I = V/R = 120/12 = 10 amperes.
Question 6: What is the primary purpose of a pressure relief valve in a hydraulic system?
- Increase system flow rate
- Filter contaminants from hydraulic fluid
- Limit maximum system pressure to prevent component damage (Correct answer)
- Control directional flow of fluid
Correct answer: Limit maximum system pressure to prevent component damage
A pressure relief valve opens when system pressure exceeds a set limit, diverting fluid back to the reservoir to protect pumps, cylinders, and lines.
Question 7: When measuring AC voltage with a multimeter, what type of value does the meter typically display?
- Peak voltage
- Peak-to-peak voltage
- RMS (root mean square) voltage (Correct answer)
- Average instantaneous voltage
Correct answer: RMS (root mean square) voltage
Standard AC voltmeters and multimeters display RMS voltage, which represents the equivalent DC heating value of the AC waveform.
CPT Electrical & Mechanical Fundamentals 2
A motor nameplate reads 460V, 3-phase.
What happens if this motor is connected to 230V, 3-phase?