Question 1

The reactance of a 35-$\mu$F capacitor connected to a 400-Hz generator is:

Accepted Answer

A)  0 Ω 
B)  0.014 Ω 
C)  0.088 Ω 
D)  11 Ω 
E)  71 Ω 
A)  0 Ω 
B)  0.014 Ω 
C)  0.088 Ω 
D)  11 Ω 
E)  71 Ω

Question 2

A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillations, the next time, after t = 0 that the energy stored in the electric field of the capacitor is a maximum is:

Accepted Answer

A)  T/4 
B)  T/2 
C)  T 
D)  3T/2 
E)  2T 
A)  T/4 
B)  T/2 
C)  T 
D)  3T/2 
E)  2T

Question 3

An RLC circuit has a resistance of 200  $\Omega$ and an inductance of 15 mH. Its oscillation frequency is 7000 Hz. At time t = 0 the current is 25 mA and there is no charge on the capacitor. After five complete cycles the current is:

Accepted Answer

A)  0 A 
B)  1.8 * 10-6 A 
C)  2.1 * 10-4 A 
D)  2.3 * 10-3 A 
E)  2.5* 10-2 A 
A)  0 A 
B)  1.8 * 10-6 A 
C)  2.1 * 10-4 A 
D)  2.3 * 10-3 A 
E)  2.5* 10-2 A

Question 4

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50-$\Omega$ resistor, a 400-mH inductor, and a 200-$\mu$F capacitor. The rms current is:

Accepted Answer

A)  0.125 A 
B)  0.135 A 
C)  0.18 A 
D)  0.20 A 
E)  0.40 A 
A)  0.125 A 
B)  0.135 A 
C)  0.18 A 
D)  0.20 A 
E)  0.40 A

Question 5

The electrical analog of a spring constant k is:

Accepted Answer

A)  L 
B)  1/L 
C)  C 
D)  1/C 
E)  R 
A)  L 
B)  1/L 
C)  C 
D)  1/C 
E)  R

Question 6

Iron, rather than copper, is used in the core of transformers because iron:

Accepted Answer

A)  can withstand a higher temperature 
B)  has a greater resistivity 
C)  has a very high permeability 
D)  makes a good permanent magnet 
E)  insulates the primary from the secondary 
A)  can withstand a higher temperature 
B)  has a greater resistivity 
C)  has a very high permeability 
D)  makes a good permanent magnet 
E)  insulates the primary from the secondary

Question 7

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50-$\Omega$ resistor, a 400-mH inductor, and a 200-$\mu$F capacitor. The rms voltage across the capacitor is:

Accepted Answer

A)  2.5 V 
B)  3.4 V 
C)  6.7 V 
D)  10.0 V 
E)  10.8 V 
A)  2.5 V 
B)  3.4 V 
C)  6.7 V 
D)  10.0 V 
E)  10.8 V

Question 8

Radio receivers are usually tuned by adjusting the capacitor of an LC circuit. If C = C1 for a frequency of 600 kHz, then for a frequency of 1200 kHz one must adjust C to:

Accepted Answer

A)  C1/2 
B)  C1/4 
C)  2C1 
D)  4C1 
E)    
A)  C1/2 
B)  C1/4 
C)  2C1 
D)  4C1 
E)

Question 9

A step-down transformer is used to:

Accepted Answer

A)  increase the power 
B)  decrease the power 
C)  increase the voltage 
D)  decrease the voltage 
E)  change ac to dc 
A)  increase the power 
B)  decrease the power 
C)  increase the voltage 
D)  decrease the voltage 
E)  change ac to dc

Question 10

An LC circuit has an inductance of 20 mH and a capacitance of 5.0 $\mu$F. At time t = 0 the charge on the capacitor is 3.0 $\mu$C and the current is 7.0 mA. The total energy is:

Accepted Answer

A)  4.1 * 10-7 J 
B)  4.9 *10-7 J 
C)  9.0 * 10-7 J 
D)  1.4 *10-6 J 
E)  2.8 * 10-6 J 
A)  4.1 * 10-7 J 
B)  4.9 *10-7 J 
C)  9.0 * 10-7 J 
D)  1.4 *10-6 J 
E)  2.8 * 10-6 J

Question 11

The angular frequency of a certain RLC series circuit is $ \omega $0. A source of sinusoidal emf, with angular frequency $ \omega $, is inserted into the circuit and $ \omega $is varied while the amplitude of the source is held constant. For which of the following values of $ \omega $is the amplitude of the current oscillations the greatest?

Accepted Answer

A)  $ \omega $0/5 
B)  $ \omega $0/2 
C) $ \omega $0 
D)  2$ \omega $0 
E)  None of them (they all produce the same current amplitude) 
A)  $ \omega $0/5 
B)  $ \omega $0/2 
C) $ \omega $0 
D)  2$ \omega $0 
E)  None of them (they all produce the same current amplitude)

Question 12

In order to maximize the rate at which energy is supplied to a resistive load, the power factor of an RLC circuit should be as close as possible to:

Accepted Answer

A)  0 
B)  0.5 
C)  1 
D)  infinity 
E)  cannot tell without knowing R, L, C, and the driving frequency 
A)  0 
B)  0.5 
C)  1 
D)  infinity 
E)  cannot tell without knowing R, L, C, and the driving frequency

Question 13

An RLC series circuit has R = 4  $\Omega$ , XC = 3  $\Omega$ , and XL = 6  $\Omega$ . The impedance of this circuit is:

Accepted Answer

A)  5  $\Omega$ 
B)  7  $\Omega$ 
C)  7.8  $\Omega$ 
D)  9.8  $\Omega$ 
E)  13  $\Omega$ 
A)  5  $\Omega$ 
B)  7  $\Omega$ 
C)  7.8  $\Omega$ 
D)  9.8  $\Omega$ 
E)  13  $\Omega$

Question 14

A 150-g block on the end of a spring with a spring constant of 35 N/m is pulled aside 25 cm and released from rest. In the electrical analog the maximum charge on the capacitor is 0.25 C. The maximum current in the LC circuit is:

Accepted Answer

A)  0.025 A 
B)  0.12 A 
C)  3.8 A 
D)  5.3 A 
E)  40 A 
A)  0.025 A 
B)  0.12 A 
C)  3.8 A 
D)  5.3 A 
E)  40 A

Question 15

An ac generator produces 10 V (rms) at 400 rad/s. It is connected to a series RL circuit (R = 17.3  $\Omega$, L = 0.025 H). The rms current is:

Accepted Answer

A)  0.50 A and leads the emf by 30 $\degree$ 
B)  0.71 A and lags the emf by 30 $\degree$ 
C)  1.4 A and lags the emf by 60 $\degree$ 
D)  0.50 A and lags the emf by 30 $\degree$ 
E)  0.58 A and leads the emf by 90 $\degree$ 
A)  0.50 A and leads the emf by 30 $\degree$ 
B)  0.71 A and lags the emf by 30 $\degree$ 
C)  1.4 A and lags the emf by 60 $\degree$ 
D)  0.50 A and lags the emf by 30 $\degree$ 
E)  0.58 A and leads the emf by 90 $\degree$

Question 16

An LC series circuit with an inductance L and a capacitance C has an oscillation frequency f. If we now take two of those inductors, each with inductance L, and two of the capacitors, each with capacitance C, and wire them all in series to make a new circuit, its oscillation frequency will be:

Accepted Answer

A)  f/4 
B)  f/2 
C)  f 
D)  2f 
E)  4f 
A)  f/4 
B)  f/2 
C)  f 
D)  2f 
E)  4f

Question 17

A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillations, the next time, after t = 0 that the charge on the capacitor is a maximum is:

Accepted Answer

A)  T/4 
B)  T/2 
C)  T 
D)  3T/2 
E)  2T 
A)  T/4 
B)  T/2 
C)  T 
D)  3T/2 
E)  2T

Question 18

An RLC series circuit, connected to a source , is at resonance. Then:

Accepted Answer

A)  the voltage across R is zero 
B)  the voltage across R equals the applied voltage 
C)  the voltage across C is zero 
D)  the voltage across L equals the applied voltage 
E)  the applied voltage and current differ in phase by 90 $\degree$ 
A)  the voltage across R is zero 
B)  the voltage across R equals the applied voltage 
C)  the voltage across C is zero 
D)  the voltage across L equals the applied voltage 
E)  the applied voltage and current differ in phase by 90 $\degree$

Question 19

The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then:

Accepted Answer

A)  the power in the primary circuit is less than that in the secondary circuit 
B)  the currents in the two circuits are the same 
C)  the voltages in the two circuits are the same 
D)  the primary current is six times the secondary current 
E)  the frequency in the secondary circuit is six times that in the primary circuit 
A)  the power in the primary circuit is less than that in the secondary circuit 
B)  the currents in the two circuits are the same 
C)  the voltages in the two circuits are the same 
D)  the primary current is six times the secondary current 
E)  the frequency in the secondary circuit is six times that in the primary circuit

Question 20

We desire to make an LC circuit that oscillates at 100 Hz using an inductance of 2.5 H. We also need a capacitance of:

Accepted Answer

A)  1 F 
B)  1 mF 
C)  1 $\mu$F 
D)  1 nF 
E)  1 pF 
A)  1 F 
B)  1 mF 
C)  1 $\mu$F 
D)  1 nF 
E)  1 pF

Exam 31: Electromagnetic Oscillations and Alternating Current

The reactance of a 35- μ\muμ F capacitor connected to a 400-Hz generator is:

A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillations, the next time, after t = 0 that the energy stored in the electric field of the capacitor is a maximum is:

An RLC circuit has a resistance of 200 Ω\OmegaΩ and an inductance of 15 mH. Its oscillation frequency is 7000 Hz. At time t = 0 the current is 25 mA and there is no charge on the capacitor. After five complete cycles the current is:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- Ω\OmegaΩ resistor, a 400-mH inductor, and a 200- μ\muμ F capacitor. The rms current is:

The electrical analog of a spring constant k is:

Iron, rather than copper, is used in the core of transformers because iron:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- Ω\OmegaΩ resistor, a 400-mH inductor, and a 200- μ\muμ F capacitor. The rms voltage across the capacitor is:

Radio receivers are usually tuned by adjusting the capacitor of an LC circuit. If C = C1 for a frequency of 600 kHz, then for a frequency of 1200 kHz one must adjust C to:

A step-down transformer is used to:

An LC circuit has an inductance of 20 mH and a capacitance of 5.0 μ\muμ F. At time t = 0 the charge on the capacitor is 3.0 μ\muμ C and the current is 7.0 mA. The total energy is:

In order to maximize the rate at which energy is supplied to a resistive load, the power factor of an RLC circuit should be as close as possible to:

An RLC series circuit has R = 4 Ω\OmegaΩ , XC = 3 Ω\OmegaΩ , and XL = 6 Ω\OmegaΩ . The impedance of this circuit is:

A 150-g block on the end of a spring with a spring constant of 35 N/m is pulled aside 25 cm and released from rest. In the electrical analog the maximum charge on the capacitor is 0.25 C. The maximum current in the LC circuit is:

An ac generator produces 10 V (rms) at 400 rad/s. It is connected to a series RL circuit (R = 17.3 Ω\OmegaΩ , L = 0.025 H). The rms current is:

An LC series circuit with an inductance L and a capacitance C has an oscillation frequency f. If we now take two of those inductors, each with inductance L, and two of the capacitors, each with capacitance C, and wire them all in series to make a new circuit, its oscillation frequency will be:

A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillations, the next time, after t = 0 that the charge on the capacitor is a maximum is:

An RLC series circuit, connected to a source , is at resonance. Then:

The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then:

We desire to make an LC circuit that oscillates at 100 Hz using an inductance of 2.5 H. We also need a capacitance of:

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The reactance of a 35- $\mu$ F capacitor connected to a 400-Hz generator is:

An RLC circuit has a resistance of 200 $\Omega$ and an inductance of 15 mH. Its oscillation frequency is 7000 Hz. At time t = 0 the current is 25 mA and there is no charge on the capacitor. After five complete cycles the current is:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- $\Omega$ resistor, a 400-mH inductor, and a 200- $\mu$ F capacitor. The rms current is:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- $\Omega$ resistor, a 400-mH inductor, and a 200- $\mu$ F capacitor. The rms voltage across the capacitor is:

Radio receivers are usually tuned by adjusting the capacitor of an LC circuit. If C = C₁ for a frequency of 600 kHz, then for a frequency of 1200 kHz one must adjust C to:

An LC circuit has an inductance of 20 mH and a capacitance of 5.0 $\mu$ F. At time t = 0 the charge on the capacitor is 3.0 $\mu$ C and the current is 7.0 mA. The total energy is:

An RLC series circuit has R = 4 $\Omega$ , X_C = 3 $\Omega$ , and X_L = 6 $\Omega$ . The impedance of this circuit is:

An ac generator produces 10 V (rms) at 400 rad/s. It is connected to a series RL circuit (R = 17.3 $\Omega$ , L = 0.025 H). The rms current is: