Mechanical Aptitude Mechanical Aptitude Basic Electrical Circuits 5 — Questions and Answers
Question 1: A transformer has 200 turns on the primary coil and 50 turns on the secondary coil. If the primary voltage is 240V, what is the secondary voltage?
- 960 volts
- 60 volts (Correct answer)
- 120 volts
- 480 volts
Correct answer: 60 volts
V_secondary = V_primary × (N_secondary / N_primary) = 240 × (50/200) = 240 × 0.25 = 60 volts.
Question 2: Which instrument would you use to check whether a circuit is open or closed without energizing it?
- Voltmeter
- Clamp meter
- Ohmmeter or continuity tester (Correct answer)
- Wattmeter
Correct answer: Ohmmeter or continuity tester
An ohmmeter or continuity tester applies its own small voltage to measure resistance, detecting open (infinite resistance) or closed (low resistance) circuits safely.
Question 3: What is the difference between AC (alternating current) and DC (direct current)?
- AC flows only in one direction; DC reverses direction periodically
- DC flows only in one direction; AC reverses direction periodically (Correct answer)
- AC has higher voltage; DC has lower voltage always
- DC requires a transformer; AC does not
Correct answer: DC flows only in one direction; AC reverses direction periodically
DC flows continuously in one direction, while AC periodically reverses direction, typically at 60 Hz in the US.
Question 4: A wire carries 3 amps for 10 seconds. How many coulombs of charge have passed through it?
- 0.3 coulombs
- 13 coulombs
- 30 coulombs (Correct answer)
- 300 coulombs
Correct answer: 30 coulombs
Charge = Current × Time = 3A × 10s = 30 coulombs.
Question 5: What is electrical 'short circuit'?
- A circuit with very high resistance throughout
- An unintended low-resistance path that allows excess current to bypass the load (Correct answer)
- A circuit with too many resistors in series
- A circuit that is too short in wire length
Correct answer: An unintended low-resistance path that allows excess current to bypass the load
A short circuit creates a direct low-resistance path, causing extremely high current that can damage wiring and start fires.
Question 6: In an electrical schematic, what does a zigzag line symbol typically represent?
- A switch
- A capacitor
- A resistor (Correct answer)
- A diode
Correct answer: A resistor
The zigzag line is the standard schematic symbol for a resistor in North American circuit diagrams.
Question 7: If you double the cross-sectional area of a wire while keeping its length and material the same, what happens to its resistance?
- Resistance doubles
- Resistance stays the same
- Resistance is halved (Correct answer)
- Resistance quadruples
Correct answer: Resistance is halved
Resistance is inversely proportional to cross-sectional area (R = ρL/A), so doubling area halves the resistance.
Mechanical Aptitude Mechanical Aptitude Basic Electrical Circuits 5
A transformer has 200 turns on the primary coil and 50 turns on the secondary coil.
If the primary voltage is 240V, what is the secondary voltage?