What is the primary focus of transient analysis in electrical circuits?
A The behavior of the circuit when conditions are stable
B The behavior of the circuit immediately after a sudden change
C The behavior of the circuit after a voltage source is turned off
D The average current in the circuit
**Transient analysis** focuses on how a circuit responds immediately after a sudden change in voltage or current. It is critical for understanding how circuits react to switching actions and abrupt disturbances.
What is the definition of steady-state in an electrical circuit?
A The condition where the voltage and current are constantly changing
B The condition where the current and voltage reach constant values
C The point at which the circuit loses energy
D The time when the energy stored in the circuit is at its peak
**Steady-state** refers to the condition in which the circuit has settled, and the voltages and currents become constant over time. This typically occurs after transient effects have subsided.
What is the primary purpose of using phasors in AC circuit analysis?
A To calculate the total power consumed
B To represent sinusoidal waveforms as complex numbers
C To calculate the total energy stored
D To represent complex DC circuits
**Phasors** simplify AC circuit analysis by converting sinusoidal voltages and currents into complex numbers. This allows for the use of algebraic methods instead of solving differential equations.
In an AC circuit, what does impedance represent?
A The total power in the circuit
B The total resistance to current flow, including reactance
C The energy stored in the circuit
D The total capacitance of the circuit
**Impedance** is the total opposition to current flow in an AC circuit, which combines both **resistance** and **reactance** (due to capacitors and inductors).
How is admittance related to impedance?
A Admittance is the inverse of impedance
B Admittance is the same as impedance
C Admittance is the sum of impedance and resistance
D Admittance is the reciprocal of resistance
**Admittance** is the reciprocal of **impedance**. While impedance measures the total opposition to current, admittance measures how easily the current flows in the circuit.
What does resonance in a series RLC circuit result in?
A Maximum impedance and minimum current
B Maximum current and minimum impedance
C Equal voltage across all components
D Minimum power consumption
**Resonance** occurs when the inductive reactance equals the capacitive reactance, resulting in minimum impedance and maximum current in the circuit.
What happens to the impedance in a purely inductive AC circuit as the frequency increases?
A It increases
B It decreases
C It remains the same
D It becomes zero
In a **purely inductive** AC circuit, the **impedance (Z)** increases with frequency because **inductive reactance (XL)** increases with frequency, following the relationship **XL = 2πfL**.
What is the result of a parallel combination of resistors?
A The total resistance increases
B The total resistance decreases
C The total resistance remains the same
D The current stays constant
In a **parallel circuit**, adding resistors provides additional paths for the current to flow, which decreases the total resistance, making it lower than the smallest individual resistance.
In an AC circuit, what happens when the power factor increases?
A The circuit becomes more efficient
B The voltage across the components decreases
C The impedance increases
D The current becomes zero
When the **power factor** increases, the circuit becomes more efficient by reducing reactive power and improving the use of real power.
What is the primary function of a transformer in an AC circuit?
A To increase or decrease frequency
B To change voltage levels
C To store electrical energy
D To convert AC to DC
A **transformer** is used to either **step-up** or **step-down** the voltage in an AC circuit, depending on the turns ratio of the transformer’s coils.
What is the unit of inductance?
A Volt
B Ampere
C Henry
D Ohm
The unit of **inductance** is the **henry (H)**. It measures an inductor’s ability to oppose changes in current flow and is essential for energy storage in the magnetic field.
What happens in an AC circuit when the frequency of the signal increases?
A The impedance of a capacitor decreases
B The impedance of an inductor decreases
C The current decreases
D The total voltage increases
As the frequency increases in an **AC circuit**, the **impedance of a capacitor (XC)** decreases because **XC = 1 / (2πfC)**, where **f** is the frequency and **C** is the capacitance.
What is the relationship between the current and voltage in a purely resistive AC circuit?
A The current and voltage are in phase
B The current leads the voltage by 90 degrees
C The current lags the voltage by 90 degrees
D The current is zero
In a **purely resistive** AC circuit, the **current and voltage are in phase**, meaning they reach their maximum and minimum values at the same time.
What happens to the total power in an AC circuit with a power factor of 1?
A The circuit becomes 100% efficient
B The current is zero
C The voltage is zero
D The impedance becomes zero
A **power factor of 1** means that all the power supplied to the circuit is being used effectively, with no power lost due to phase difference between current and voltage, making the circuit 100% efficient.
What is the main role of a capacitor in a DC circuit after a long time?
A It behaves like an open circuit
B It behaves like a short circuit
C It allows current to flow continuously
D It blocks all current
In a **DC circuit**, after a long time, the **capacitor** becomes fully charged and behaves like an open circuit, preventing current flow.
What is the effect of increasing impedance in a circuit?
A The current decreases
B The current increases
C The total power increases
D The voltage decreases
According to **Ohm’s Law**, if the **impedance** in a circuit increases, the current decreases, assuming that the voltage remains constant.
What is the effect of resonance on current in a series RLC circuit?
A The current increases
B The current decreases
C The current remains constant
D The current becomes zero
At **resonance** in a **series RLC circuit**, the impedance is minimized, and the current is maximized. This occurs when the inductive and capacitive reactances cancel each other out.
What happens in a parallel circuit when more resistors are added?
A The total current decreases
B The total current increases
C The total resistance increases
D The voltage across each component decreases
In a **parallel circuit**, adding more resistors provides more paths for current to flow, which increases the total current supplied by the source. The total resistance decreases as more resistors are added.
What does the power factor in an AC circuit measure?
A The ratio of voltage to current
B The ratio of real power to apparent power
C The current in the circuit
D The phase difference between current and voltage
The **power factor** is the ratio of **real power** (useful power) to **apparent power** (total power). A power factor of 1 means the circuit is operating at maximum efficiency with no reactive power.
What is the function of a transformer in an electrical circuit?
A To store energy
B To change voltage levels
C To convert AC to DC
D To regulate current
A **transformer** changes the **voltage level** in an AC circuit, either stepping up or stepping down the voltage depending on the turns ratio of the primary and secondary coils.