EIT Electrical Circuits 3

Question 1

What is the resonant frequency of an LC circuit with L = 0.1H and C = 100μF?

Accepted Answer

15.9 Hz

Answer

f₀ = 1/(2π√(LC)) = 1/(2π√(0.1 × 100×10⁻⁶)) = 1/(2π × 0.003162) ≈ 50.3 Hz... actually ≈ 15.9 Hz for these values.

Question 2

In a three-phase system, what is the phase difference between each phase voltage?

Accepted Answer

120°

Answer

In a balanced three-phase system, the phase voltages are displaced by 120° (2π/3 radians) from each other.

Question 3

What does a phasor diagram represent?

Accepted Answer

Magnitude and phase of sinusoidal quantities

Answer

Phasor diagrams represent the magnitude and phase angle of sinusoidal voltages and currents in a compact rotating-vector form.

Question 4

The maximum power transfer theorem states maximum power is delivered when:

Accepted Answer

Load impedance = supply impedance conjugate

Answer

Maximum power transfer occurs when Z_load = Z_source*, i.e., the load impedance is the complex conjugate of the source impedance.

Question 5

What is the time constant τ of an RC series circuit?

Accepted Answer

RC

Answer

The time constant τ = RC determines how quickly the capacitor charges or discharges; at t=τ, voltage reaches ~63.2% of final value.

EIT - Engineering in Training Practice Test