Conceptual Questions 2 Flashcards
In an AC circuit with resistive, inductive, and capacitive elements, define complex power.
How does the power factor relate to the real, reactive, and apparent power in the power
triangle? What value of power factor indicates the maximum efficiency?
: Complex power in an AC circuit combines real power, which does actual work, and
reactive power, which oscillates between the source and reactive components. It is expressed as
𝑆=𝑃+𝑗𝑄S=P+jQ.
The power factor (PF) is the cosine of the phase angle between voltage and current,
representing how efficiently power is used. A PF of 1 indicates maximum efficiency with no
reactive power.
The power triangle visually represents this relationship, with P as the horizontal side, Q as the
vertical side, and the hypotenuse as the apparent power (𝑆S)
How does the superposition principle facilitate the analysis of circuits with multiple independent sources, and what are its limitations?
The superposition principle states that the voltage or current in any branch of a linear
circuit with multiple sources is the algebraic sum of the voltages or currents caused by each
source independently. It is not applicable to power calculations or in non-linear circuits.
How does the time constant of an RC (resistor-capacitor) circuit affect the charging and
discharging process of the capacitor?
The time constant of an RC circuit (represented as τ = RC defines how quickly the
capacitor charges to 63.2% of the supply voltage or discharges to 36.8% of its initial voltage.
: What role do inductors play in a circuit, and how does their behavior contrast with that of
capacitors over time?
Inductors resist changes in current, storing energy in a magnetic field. Unlike capacitors, which store energy in an electric field and resist changes in voltage, inductors release energy
when the current decreases
What effect does the frequency of an AC source have on the impedance of capacitive and
inductive elements within the circuit?
The impedance of capacitive elements decreases with increasing frequency, while the
impedance of inductive elements increases with increasing frequency.
Why does a non-zero phase difference between voltage and current indicate the presence
of reactive power in an AC circuit?
A non-zero phase difference indicates the presence of reactive power, which means that
the voltage and current are not in phase, and energy is stored temporarily in the circuit elements
What is the effect of doubling the resistance or capacitance on the time constant and
transient response of an RC circuit?
Doubling the resistance or capacitance doubles the time constant, τ, which slows down
the rate of voltage and current change during transient conditions.
Why is the voltage across a capacitor not able to change instantaneously in response to a
step input?
A capacitor cannot change its voltage instantaneously due to its ability to store energy,
which requires time to charge or discharge through the resistive element.
How do you verify the correctness of Thevenin’s and Norton’s equivalents through
simulation and experimentation?
To verify Thevenin’s and Norton’s equivalents, you can use circuit simulation software to
compare the behavior of the original circuit with the simplified equivalent circuit under various
loading conditions. Experimentally, measurements can be made to ensure the responses match.
What are the limitations of Thevenin’s and Norton’s Theorems when applied to non-linear
and time-variant circuits?
These theorems are limited to linear, time-invariant circuits. They do not apply directly
to circuits with nonlinear elements or where circuit parameters change over time
Explain why it is necessary to turn off all independent sources when calculating Thevenin’s
and Norton’s equivalent circuits.
Independent sources must be turned off to focus on the intrinsic properties of the
circuit, isolating the network’s response based solely on its passive component
: How does the principle of balance in a Wheatstone Bridge allow for the precise
measurement of unknown resistances, and what are the implications of bridge imbalance on
measurement accuracy?
A Wheatstone Bridge measures unknown resistance by balancing two ratioed
resistances. When balanced, the voltage between the midpoints is zero, indicating the unknown
resistance equals the product over the sum of the other three. Imbalance leads to voltage across
the midpoints, reducing measurement accuracy.
