Question 1

A capacitor, initially charged, and an inductor form an LC circuit. When the electric current in the circuit is equal to zero how much energy is stored on each device?
A)Inductor: zero energy. Capacitor: zero energy
B)Inductor: Half of the maximum energy. Capacitor: Half of the maximum energy
C)Inductor: maximum energy. Capacitor: zero energy
D)Inductor: zero energy. Capacitor: maximum energy
E)Inductor: maximum energy. Capacitor: maximum energy

Accepted Answer

In an LC circuit, when the current is zero, all the energy is stored in the capacitor as electric potential energy, and none is stored in the inductor.

Question 2

In a series LRC circuit, Kirchhoff's loop rule
A)is obeyed.
B)would be obeyed but the voltages are not in phase.
C)would be obeyed but the currents and voltages are not in phase.
D)is not obeyed.
E)would be obeyed but the currents are not in phase.

Accepted Answer

Kirchhoff's loop rule is obeyed in a series LRC circuit because the sum of the voltages around the loop is equal to zero. This is because the voltage across the inductor is equal and opposite to the voltage across the capacitor, and the voltage across the resistor is equal to the sum of the voltages across the inductor and capacitor.

Question 3

In an LRC circuit, if the condition R² = L/C holds, the circuit is A)overdamped. B)not affected. C)underdamped. D)totally inundated. E)critically damped.

Accepted Answer

The answer of In an LRC circuit, if the condition...

Question 4

A pure capacitor is connected to an ac power supply. In this circuit, the current
A)leads the voltage by 90°.
B)lags the voltage by 90°.
C)lags the voltage by 180°.
D)is in phase with the voltage.
E)none of the given answers

Accepted Answer

In a pure capacitor circuit, the current leads the voltage by 90 degrees.

Question 5

As the frequency of the ac voltage across an inductor approaches zero, the inductive reactance of that coil
A)approaches zero.
B)approaches infinity.
C)approaches unity.
D)none of the given answers

Accepted Answer

Inductive reactance (X_L) is given by the formula X_L = 2πfL, where f is the frequency and L is the inductance. As the frequency approaches zero, the inductive reactance also approaches zero.

Question 6

In a pure resistive circuit, the phase angle between current and voltage is
A)0.
B)π/2 radians.
C)-π/2 radians.
D)π radians.
E)3π/4 radians.

Accepted Answer

In a pure resistive circuit, the voltage and current are in phase with each other, meaning the phase angle between them is 0 radians.

Question 7

Consider a capacitor connected across the ac supply. The current through the capacitor will ________ as the capacitance is increased.
A)increase
B)remain constant
C)decrease

Accepted Answer

The current through a capacitor in an AC circuit is given by I = VωC, where V is the voltage, ω is the angular frequency, and C is the capacitance. As the capacitance increases, the current also increases.

Question 8

An electric circuit consists of a resistor connected across the terminals of an ac generator. How does the power dissipated in the resistor change as the frequency in the generator decreases?
A)It decreases.
B)It increases.
C)It does not change.
D)It increases or decreases depending on the sign of the phase angle.

Accepted Answer

The answer of An electric circuit consists of a resistor...

Question 9

What is the phase angle between the voltages of the inductor and capacitor in a LRC series circuit?
A)zero
B)45°
C)90°
D)180°
E)270°

Accepted Answer

In a series LRC circuit, the voltage across the inductor leads the current by 90°, and the voltage across the capacitor lags the current by 90°. Therefore, the phase angle between the voltages of the inductor and capacitor is 180°.

Question 10

A pure inductor is connected to an ac power supply. In this circuit, the current
A)leads the voltage by 90°.
B)is in phase with the voltage.
C)lags the voltage by 45°.
D)lags the voltage by 90°.
E)leads the voltage by 45°.

Accepted Answer

In a pure inductor, the current lags the voltage by 90°. This is because the inductor opposes changes in the current through it, and the voltage across an inductor is proportional to the rate of change of the current. In an AC circuit, the voltage is constantly changing, so the current lags behind it by 90°.

Question 11

Consider 2 LRC circuits at critical damping. In which circuit does the initial charge on the capacitor decrease to 10% of its value the fastest?
A)in the circuit with the smallest initial charge on the capacitor
B)in the circuit with the largest resistance
C)in the circuit with the largest LC product
D)in the circuit with the smallest LC product
E)in the circuit with the largest initial charge on the capacitor

Accepted Answer

The answer of Consider 2 LRC circuits at critical damping....

Question 12

The average energy dissipated in an inductor is
A)zero.
B)proportional to the inductance.
C)proportional to both the inductance and frequency.
D)proportional to the frequency.
E)none of the above.

Accepted Answer

The average energy dissipated in an ideal inductor is zero because inductors store energy in their magnetic field and release it back to the circuit, without dissipating it as heat.

Question 13

A resistor is connected to an ac power supply. On this circuit, the current
A)leads the voltage by 90°.
B)lags the voltage by 90°.
C)is in phase with the voltage.
D)leads the voltage by 45°.
E)lags the voltage by 45°.

Accepted Answer

In a purely resistive AC circuit, the current is in phase with the voltage, meaning they reach their maximum and zero values simultaneously.

Question 14

An LRC circuit has component values such that the circuit is initially at critical damping. Which of the following modifications would make the circuit underdamped?
A)decreasing the capacitance C, keeping the inductance L and the resistance R the same
B)reducing both the inductance and the capacitance by half, keeping the resistance R the same
C)increasing the resistance R, keeping the inductance L and the capacitance C the same
D)doubling both the inductance and the capacitance, keeping the resistance R the same
E)decreasing the inductance L, keeping the capacitance C and the resistance R the same

Accepted Answer

The answer of An LRC circuit has component values such...

Question 15

The energy transformed in an inductor during a portion of a cycle
A)is always positive.
B)may be positive, negative, or zero.
C)is always negative.
D)is always zero.
E)is never zero.

Accepted Answer

The energy in an inductor can be positive, negative, or zero depending on the phase of the AC cycle, as energy is stored in the magnetic field and can be returned to the circuit.

Question 16

Consider an LRC circuit. The impedance of the circuit increases if X_L increases. When is this statement true? A)always true B)true only if X_L is equal to X_C C)true only if X_L is less than X_C D)true only if X_L is greater than or equal to X_C E)never true

Accepted Answer

The impedance of an LRC circuit is given by Z = √(R² + (X_L - X_C)²). If X_L increases and is greater than or equal to X_C, the term (X_L - X_C) increases, thus increasing the impedance.

Question 17

An ac source of period T and maximum voltage V is connected to a single unknown element. At time t = 0 the voltage is zero. At time t = T/4 the current in the unknown element is equal to zero, and at time t = T/2 the current is I = - I_max where I_max is the current amplitude. What is the unknown element? A)a resistor B)an inductor C)a capacitor D)an inductor or a capacitor E)More information is needed to identify the element.

Accepted Answer

The current in a capacitor leads the voltage by 90 degrees. At t = T/4, the voltage is at its maximum, and the current is zero, which is consistent with a capacitor. At t = T/2, the voltage is zero, and the current is at its negative maximum, which also matches the behavior of a capacitor.

Question 18

Consider an LRC circuit. The impedance of the circuit increases if R increases. When is this statement true? A)always true B)true only if X_L is less than or equal to X_C C)true only if X_L is greater than or equal to X_C D)true only if X_L is equal to X_C E)never true

Accepted Answer

The impedance of an LRC circuit is given by Z = √(R² + (X_L - X_C)²). Increasing R always increases the value of Z, regardless of the values of X_L and X_C.

Question 19

In each element of a series LRC circuit
A)the currents are not in phase.
B)the currents and voltages are not in phase.
C)the voltages are in phase.
D)the currents are in phase.
E)the currents and voltages are in phase.

Accepted Answer

The answer of In each element of a series LRC...

Question 20

As the frequency of the ac voltage across a capacitor approaches zero, the capacitive reactance of that capacitor
A)approaches zero.
B)approaches infinity.
C)approaches unity.
D)none of the given answers

Accepted Answer

As the frequency approaches zero, the capacitive reactance, which is inversely proportional to frequency, approaches infinity.

Quiz 30: Inductance, Electromagnetic Oscillations, and Ac Circuits

A capacitor, initially charged, and an inductor form an LC circuit. When the electric current in the circuit is equal to zero how much energy is stored on each device?

In a series LRC circuit, Kirchhoff's loop rule

In an LRC circuit, if the condition R2 = L/C holds, the circuit is

A pure capacitor is connected to an ac power supply. In this circuit, the current

As the frequency of the ac voltage across an inductor approaches zero, the inductive reactance of that coil

In a pure resistive circuit, the phase angle between current and voltage is

Consider a capacitor connected across the ac supply. The current through the capacitor will ________ as the capacitance is increased.

An electric circuit consists of a resistor connected across the terminals of an ac generator. How does the power dissipated in the resistor change as the frequency in the generator decreases?

What is the phase angle between the voltages of the inductor and capacitor in a LRC series circuit?

A pure inductor is connected to an ac power supply. In this circuit, the current

Consider 2 LRC circuits at critical damping. In which circuit does the initial charge on the capacitor decrease to 10% of its value the fastest?

The average energy dissipated in an inductor is

A resistor is connected to an ac power supply. On this circuit, the current

An LRC circuit has component values such that the circuit is initially at critical damping. Which of the following modifications would make the circuit underdamped?

The energy transformed in an inductor during a portion of a cycle

Consider an LRC circuit. The impedance of the circuit increases if XL increases. When is this statement true?

Consider an LRC circuit. The impedance of the circuit increases if R increases. When is this statement true?

In each element of a series LRC circuit

As the frequency of the ac voltage across a capacitor approaches zero, the capacitive reactance of that capacitor

In an LRC circuit, if the condition R² = L/C holds, the circuit is

Consider an LRC circuit. The impedance of the circuit increases if X_L increases. When is this statement true?