Electrical Theory & Fundamentals Flashcards

A 1,500 W electric heater operates for 8 hours. How many kWh does it consume?

Answer: 12 kWh

Energy = Power × Time = 1.5 kW × 8 h = 12 kWh.

Which of the following best describes semiconductors?

Answer: Materials with conductivity between conductors and insulators

Semiconductors like silicon have electrical conductivity that can be controlled, placing them between conductors and insulators.

What is the effect of doubling the cross-sectional area of a conductor while keeping length and material constant?

Answer: Resistance is halved

R = ρL/A; doubling area (A) halves resistance, allowing more current to flow.

What voltage is typically found on a standard US residential 240V circuit?

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.

What does the term 'electromotive force' (EMF) refer to?

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.

A circuit breaker trips repeatedly on a 20A circuit. After confirming no short circuit, which is the most likely cause?

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.

What is the phase relationship between voltage and current in a purely resistive AC circuit?

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.