CEA Electrical Theory & Fundamentals 5 — Questions and Answers
Question 1: A 1,500 W electric heater operates for 8 hours. How many kWh does it consume?
- 10 kWh
- 12 kWh (Correct answer)
- 8 kWh
- 15 kWh
Correct answer: 12 kWh
Energy = Power × Time = 1.5 kW × 8 h = 12 kWh.
Question 2: Which of the following best describes semiconductors?
- Materials with zero resistance
- Materials that only conduct at high temperatures
- Materials with conductivity between conductors and insulators (Correct answer)
- Materials that block all current flow
Correct answer: Materials with conductivity between conductors and insulators
Semiconductors like silicon have electrical conductivity that can be controlled, placing them between conductors and insulators.
Question 3: What is the effect of doubling the cross-sectional area of a conductor while keeping length and material constant?
- Resistance doubles
- Resistance is halved (Correct answer)
- Resistance stays the same
- Resistance quadruples
Correct answer: Resistance is halved
R = ρL/A; doubling area (A) halves resistance, allowing more current to flow.
Question 4: What voltage is typically found on a standard US residential 240V circuit?
- Two 120 V legs that are in phase
- Two 120 V legs that are 180° out of phase (Correct answer)
- One 240 V leg and a neutral
- Three 120 V legs 120° apart
Correct answer: Two 120 V legs that are 180° out of phase
US 240V service uses two 120V hot conductors that are 180° out of phase, producing 240V between them.
Question 5: What does the term 'electromotive force' (EMF) refer to?
- The force exerted on a conductor in a magnetic field
- The voltage produced by a source driving current through a circuit (Correct answer)
- The opposition to current flow
- The rate of energy dissipation
Correct answer: The voltage produced by a source driving current through a circuit
EMF is the voltage generated by a source (battery, generator) that drives current around a circuit.
Question 6: A circuit breaker trips repeatedly on a 20A circuit. After confirming no short circuit, which is the most likely cause?
- Voltage is too low
- Circuit is overloaded beyond 20A capacity (Correct answer)
- Neutral wire is loose
- Ground fault only
Correct answer: Circuit is overloaded beyond 20A capacity
Repeated tripping without a short circuit indicates the connected loads draw more current than the 20A breaker allows.
Question 7: What is the phase relationship between voltage and current in a purely resistive AC circuit?
- Current leads voltage by 90°
- Voltage leads current by 90°
- Voltage and current are in phase (Correct answer)
- They are 180° out of phase
Correct answer: Voltage and current are in phase
In a purely resistive circuit, voltage and current rise and fall together, so they are perfectly in phase.
CEA Electrical Theory & Fundamentals 5
A 1,500 W electric heater operates for 8 hours.
How many kWh does it consume?