FREE HAM Radio Extra Class Test Advanced Electrical Principles Questions and Answers

Question 1

In a series RLC circuit at resonance, what is the phase relationship between the current and the applied voltage?

Accepted Answer

The current and voltage are in phase.

Answer

At the resonant frequency in a series RLC circuit, the inductive reactance (XL) and capacitive reactance (XC) are equal and cancel each other out. This leaves only the resistance (R) to impede the current. In a purely resistive circuit, the current and voltage are in phase.

Question 2

What is the time constant of a series RL circuit containing a 100-ohm resistor and a 20-mH inductor?

Accepted Answer

0.2 milliseconds

Answer

The time constant (τ) of a series RL circuit is calculated by dividing the inductance (L) by the resistance (R). In this case, τ = L / R = 0.020 H / 100 Ω = 0.0002 seconds, which is equal to 0.2 milliseconds.

Question 3

Which of the following describes the impedance of a parallel RLC circuit at its resonant frequency?

Accepted Answer

It is at its maximum value.

Answer

In a parallel RLC circuit, at the resonant frequency, the inductive and capacitive susceptances are equal and opposite, canceling each other out. This results in a purely resistive circuit with the impedance at its maximum value. This is why a parallel resonant circuit is often called a rejector circuit.

Question 4

A circuit has an impedance represented by the complex number 30 + j40 ohms. What is the phase angle of the voltage with respect to the current?

Accepted Answer

53.1 degrees leading

Answer

The phase angle (θ) can be found using the arctangent of the reactive part (imaginary) divided by the resistive part (real). So, θ = arctan(40/30) = arctan(1.333) ≈ 53.1 degrees. Since the reactive component (+j40) is positive, it is inductive, and in an inductive circuit, the voltage leads the current.

Question 5

In a circuit containing both a resistor and a capacitor connected in series to an AC source, what is the relationship between the current and the voltage?

Accepted Answer

Current leads the voltage.

Answer

In a capacitive circuit, the current must flow to charge the plates of the capacitor before a voltage can build up across it. Therefore, in a series RC circuit, the current leads the voltage. The mnemonic 'ICE' (Current leads Voltage in a Capacitive circuit) can be helpful.

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

FREE HAM Radio Extra Class Test Advanced Electrical Principles Questions and Answers