Advanced Electrical Principles Flashcards
6 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Advanced Electrical Principles flashcards as text
In a series RLC circuit at resonance, what is the phase relationship between the current and the applied voltage?
Answer: The current and voltage are in phase.
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.
What is the time constant of a series RL circuit containing a 100-ohm resistor and a 20-mH inductor?
Answer: 0.2 milliseconds
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.
Which of the following describes the impedance of a parallel RLC circuit at its resonant frequency?
Answer: It is at its maximum value.
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.
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?
Answer: 53.1 degrees leading
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.
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?
Answer: Current leads the voltage.
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.
What is the resonant frequency of a series circuit with a 10 µH inductor and a 25 pF capacitor?
Answer: 10.1 MHz
The resonant frequency (f_r) of an LC circuit is calculated using the formula f_r = 1 / (2 * π * sqrt(L * C)). Plugging in the values: f_r = 1 / (2 * π * sqrt(10e-6 H * 25e-12 F)) = 1 / (2 * π * sqrt(250e-18)) = 1 / (2 * π * 15.81e-9) ≈ 10.06 MHz.