Question 1

A charged 200- $\mu$ F capacitor is connected to a 100-mH inductor to form an LC oscillator. The voltage across the inductor oscillates at

Accepted Answer

A)  210 Hz. 
B)  120 Hz. 
C)  36 Hz. 
D)  82 Hz. 
A)  210 Hz. 
B)  120 Hz. 
C)  36 Hz. 
D)  82 Hz.

Question 2

As the impedance in a simple series AC circuit gets larger, all of the following statements are valid except

Accepted Answer

A)  for a given AC current, the AC voltage increases. 
B)  for a given AC power, the AC current decreases. 
C)  for a given AC voltage, the AC current decreases. 
D)  for a given AC voltage, the AC power increases. 
A)  for a given AC current, the AC voltage increases. 
B)  for a given AC power, the AC current decreases. 
C)  for a given AC voltage, the AC current decreases. 
D)  for a given AC voltage, the AC power increases.

Question 3

In a simple series AC circuit, an explanation for the phase relationship between current and voltage for a capacitor is that the voltage across a capacitor is proportional to

Accepted Answer

A)  the current. 
B)  the time integral of the current. 
C)  the time derivative of the current. 
D)  none of the above. 
A)  the current. 
B)  the time integral of the current. 
C)  the time derivative of the current. 
D)  none of the above.

Question 4

The power factor for an RLC circuit is

Accepted Answer

A)  sin $\theta$ . 
B)  cos $\theta$ 
C)  tan $\theta$ 
D)  cot $\theta$ 
A)  sin $\theta$ . 
B)  cos $\theta$ 
C)  tan $\theta$ 
D)  cot $\theta$

Question 5

A transformer has 90 turns on the primary coil and 175 turns on the secondary coil. If the AC input current is 5 A, the output current is

Accepted Answer

A)  2.6 A. 
B)  9.7 A. 
C)  3.5 A. 
D)  7.8 A. 
A)  2.6 A. 
B)  9.7 A. 
C)  3.5 A. 
D)  7.8 A.

Question 6

Consider an ideal inductor L connected directly to an AC voltage source V, with I being the current in the loop. Summing voltage drops around the loop yields

Accepted Answer

A)  $d I / d t = V / L$ 
B)  $d V / d t = I / L$ 
C)  $d V / d t = L / I$ 
D)  $d I / d t = L / V$ 
A)  $d I / d t = V / L$ 
B)  $d V / d t = I / L$ 
C)  $d V / d t = L / I$ 
D)  $d I / d t = L / V$

Question 7

The resonant frequency of a 1-H inductor and 1-F capacitor (forming an LC circuit) is

Accepted Answer

A)  0.16 Hz. 
B)  1 Hz. 
C)  1.2 Hz. 
D)  1.4 Hz. 
A)  0.16 Hz. 
B)  1 Hz. 
C)  1.2 Hz. 
D)  1.4 Hz.

Question 8

The maximum (instantaneous) emf across a capacitor is 160 V and the reactance of the capacitor is 12 $\Omega$ . The maximum current through the capacitor is

Accepted Answer

A)  22 A. 
B)  77 mA. 
C)  13 A. 
D)  5.2 A. 
A)  22 A. 
B)  77 mA. 
C)  13 A. 
D)  5.2 A.

Question 9

In a simple series RC circuit with a sinusoidal driving voltage, the phase relationship for a capacitor is that the

Accepted Answer

A)  current leads the voltage by 90°. 
B)  voltage leads the current by 90°. 
C)  Either response might be correct, depending on further details. 
D)  The voltage and current are in phase. 
A)  current leads the voltage by 90°. 
B)  voltage leads the current by 90°. 
C)  Either response might be correct, depending on further details. 
D)  The voltage and current are in phase.

Question 10

The rms emf across an inductor is 5.2 V, and the reactance of the inductor is 0.77 $\Omega$ . The current (rms) through the inductor is

Accepted Answer

A)  1.5 A. 
B)  6.8 A. 
C)  510 mA. 
D)  150 mA. 
A)  1.5 A. 
B)  6.8 A. 
C)  510 mA. 
D)  150 mA.

Question 11

RMS voltage is related to peak voltage by the equation

Accepted Answer

A)  Vrms = Vpeak. 
B)  Vrms = Vpeak/ $\sqrt { 2 }$ . 
C)  Vrms = Vpeak/2. 
D)  Vrms = Vpeak/4. 
A)  Vrms = Vpeak. 
B)  Vrms = Vpeak/ $\sqrt { 2 }$ . 
C)  Vrms = Vpeak/2. 
D)  Vrms = Vpeak/4.

Question 12

An RLC circuit has a 12- $\Omega$ resistor connected to an inductor with 44 $\Omega$ reactance and a capacitor with 21 $\Omega$ reactance. The effective resistance as seen by the source (impedance) is

Accepted Answer

A)  26 $\Omega$ 
B)  12 $\Omega$ 
C)  23 $\Omega$ 
D)  21 $\Omega$ 
A)  26 $\Omega$ 
B)  12 $\Omega$ 
C)  23 $\Omega$ 
D)  21 $\Omega$

Question 13

A possible clue to question 35 is that the electrical element that exhibits "inertia to the change of the current" is the

Accepted Answer

A)  inductor. 
B)  capacitor. 
C)  Either of the previous responses is valid. 
D)  None of the previous responses is valid. 
A)  inductor. 
B)  capacitor. 
C)  Either of the previous responses is valid. 
D)  None of the previous responses is valid.

Question 14

A transformer has 90 turns on the primary coil and 175 turns on the secondary coil. If the input voltage is 120 VAC, the output voltage is

Accepted Answer

A)  62 VAC. 
B)  92 VAC. 
C)  230 VAC. 
D)  180 VAC. 
A)  62 VAC. 
B)  92 VAC. 
C)  230 VAC. 
D)  180 VAC.

Question 15

In the transfer of electrical energy over power lines, it is desirable to minimize Joule heating. Therefore it is desirable to reduce the

Accepted Answer

A)  resistance. 
B)  voltage. 
C)  current. 
D)  both (a) and (c). 
A)  resistance. 
B)  voltage. 
C)  current. 
D)  both (a) and (c).

Question 16

In an ideal transformer, the output

Accepted Answer

A)  voltage cannot exceed the input voltage. 
B)  current cannot exceed the input current. 
C)  power cannot exceed the input power. 
D)  Each of the previous responses is valid. 
A)  voltage cannot exceed the input voltage. 
B)  current cannot exceed the input current. 
C)  power cannot exceed the input power. 
D)  Each of the previous responses is valid.

Question 17

At high frequencies, the reactances of an inductor and capacitor are

Accepted Answer

A)  both large. 
B)  large and small, respectively. 
C)  small and large, respectively. 
D)  both small. 
A)  both large. 
B)  large and small, respectively. 
C)  small and large, respectively. 
D)  both small.

Question 18

The quality factor, Q, of an ideal LC circuit oscillating at $\omega _ { 0 } = 100$ rad/s with an inductor (L) of 120 mH is

Accepted Answer

A)  120. 
B) 6/5. 
C)  100 
D) infinite. 
A)  120. 
B) 6/5. 
C)  100 
D) infinite.

Question 19

A 45-VAC signal (rms) is present across a 5- $\Omega$ resistor. The time-averaged power dissipated in the resistor is

Accepted Answer

A)  400 W. 
B)  800 W. 
C)  200 W. 
D)  100 W. 
A)  400 W. 
B)  800 W. 
C)  200 W. 
D)  100 W.

Question 20

The instantaneous power loss in a circuit containing a resistor and an inductor through which DC current flows is given by the formula P = I2 Z. To retain the form of this equation for the case of AC current, it is enough to

Accepted Answer

A)  interpret P as average power. 
B)  interpret I as rms current. 
C)  Both of the first two answers are necessary and sufficient. 
D)  Both of the first two answers are necessary, but they are not sufficient. 
A)  interpret P as average power. 
B)  interpret I as rms current. 
C)  Both of the first two answers are necessary and sufficient. 
D)  Both of the first two answers are necessary, but they are not sufficient.

Exam 32: Alternating Current Circuits

A charged 200- μ\muμ F capacitor is connected to a 100-mH inductor to form an LC oscillator. The voltage across the inductor oscillates at

As the impedance in a simple series AC circuit gets larger, all of the following statements are valid except

In a simple series AC circuit, an explanation for the phase relationship between current and voltage for a capacitor is that the voltage across a capacitor is proportional to

The power factor for an RLC circuit is

A transformer has 90 turns on the primary coil and 175 turns on the secondary coil. If the AC input current is 5 A, the output current is

Consider an ideal inductor L connected directly to an AC voltage source V, with I being the current in the loop. Summing voltage drops around the loop yields

The resonant frequency of a 1-H inductor and 1-F capacitor (forming an LC circuit) is

The maximum (instantaneous) emf across a capacitor is 160 V and the reactance of the capacitor is 12 Ω\OmegaΩ . The maximum current through the capacitor is

In a simple series RC circuit with a sinusoidal driving voltage, the phase relationship for a capacitor is that the

The rms emf across an inductor is 5.2 V, and the reactance of the inductor is 0.77 Ω\OmegaΩ . The current (rms) through the inductor is

RMS voltage is related to peak voltage by the equation

An RLC circuit has a 12- Ω\OmegaΩ resistor connected to an inductor with 44 Ω\OmegaΩ reactance and a capacitor with 21 Ω\OmegaΩ reactance. The effective resistance as seen by the source (impedance) is

A possible clue to question 35 is that the electrical element that exhibits "inertia to the change of the current" is the

A transformer has 90 turns on the primary coil and 175 turns on the secondary coil. If the input voltage is 120 VAC, the output voltage is

In the transfer of electrical energy over power lines, it is desirable to minimize Joule heating. Therefore it is desirable to reduce the

In an ideal transformer, the output

At high frequencies, the reactances of an inductor and capacitor are

The quality factor, Q, of an ideal LC circuit oscillating at ω0=100\omega _ { 0 } = 100ω0​=100 rad/s with an inductor (L) of 120 mH is

A 45-VAC signal (rms) is present across a 5- Ω\OmegaΩ resistor. The time-averaged power dissipated in the resistor is

The instantaneous power loss in a circuit containing a resistor and an inductor through which DC current flows is given by the formula P = I2 Z. To retain the form of this equation for the case of AC current, it is enough to

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