Question 1

When the frequency of the oscillator in a series RLC circuit is doubled:

Accepted Answer

A)  the capacitive reactance is doubled 
B)  the capacitive reactance is halved 
C)  the impedance is doubled 
D)  the current amplitude is doubled 
E)  the current amplitude is halved 
A)  the capacitive reactance is doubled 
B)  the capacitive reactance is halved 
C)  the impedance is doubled 
D)  the current amplitude is doubled 
E)  the current amplitude is halved

Question 2

The total energy in an LC circuit is 5.0 *10-6 J. If C = 15 $\mu$F the maximum charge on the capacitor is:

Accepted Answer

A)  0.82 $\mu$C 
B)  8.5 $\mu$C 
C)  12 $\mu$C 
D)  17 $\mu$C 
E)  24$\mu$C 
A)  0.82 $\mu$C 
B)  8.5 $\mu$C 
C)  12 $\mu$C 
D)  17 $\mu$C 
E)  24$\mu$C

Question 3

In a sinusoidally driven series RLC circuit the current lags the applied emf. The rate at which energy is dissipated in the resistor can be increased by:

Accepted Answer

A)  decreasing the capacitance and making no other changes 
B)  increasing the capacitance and making no other changes 
C)  increasing the inductance and making no other changes 
D)  increasing the driving frequency and making no other changes 
E)  decreasing the amplitude of the driving emf and making no other changes 
A)  decreasing the capacitance and making no other changes 
B)  increasing the capacitance and making no other changes 
C)  increasing the inductance and making no other changes 
D)  increasing the driving frequency and making no other changes 
E)  decreasing the amplitude of the driving emf and making no other changes

Question 4

An LC circuit has a capacitance of 30$\mu$F and an inductance of 15 mH. At time t = 0 the charge on the capacitor is 10 $\mu$C and the current is 20 mA. The maximum charge on the capacitor is:

Accepted Answer

A)  8.9 $\mu$C 
B)  10 $\mu$C 
C)  12 $\mu$C 
D)  17 $\mu$C 
E)  24 $\mu$C 
A)  8.9 $\mu$C 
B)  10 $\mu$C 
C)  12 $\mu$C 
D)  17 $\mu$C 
E)  24 $\mu$C

Question 5

A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 $\mu$J. At a certain instant the energy in the capacitor is 40 $\mu$J. At that instant what is the emf induced in the inductor?

Accepted Answer

A)  0 V 
B)  5 V 
C)  10 V 
D)  15 V 
E)  20 V 
A)  0 V 
B)  5 V 
C)  10 V 
D)  15 V 
E)  20 V

Question 6

A coil has a resistance of 60  $\Omega$  and an impedance of 100  $\Omega$ . Its reactance is:

Accepted Answer

A)  40  $\Omega$ 
B)  60  $\Omega$ 
C)  80  $\Omega$ 
D)  117 $\Omega$ 
E)  160  $\Omega$ 
A)  40  $\Omega$ 
B)  60  $\Omega$ 
C)  80  $\Omega$ 
D)  117 $\Omega$ 
E)  160  $\Omega$

Question 7

The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. If R is connected directly to the source it will dissipate a power of:

Accepted Answer

A)  P/9 
B)  P/3 
C)  P 
D)  3P 
E)  9P 
A)  P/9 
B)  P/3 
C)  P 
D)  3P 
E)  9P

Question 8

The impedance of an RLC series circuit is definitely increased if:

Accepted Answer

A)  C decreases 
B)  L increases 
C)  L decreases 
D)  R increases 
E)  R decreases 
A)  C decreases 
B)  L increases 
C)  L decreases 
D)  R increases 
E)  R decreases

Question 9

In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is:

Accepted Answer

A)  25,600 V 
B)  3200 V 
C)  400 V 
D)  50 V 
E)  6.25 V 
A)  25,600 V 
B)  3200 V 
C)  400 V 
D)  50 V 
E)  6.25 V

Question 10

When the amplitude of the oscillator in a series RLC circuit is doubled:

Accepted Answer

A)  the impedance is doubled 
B)  the voltage across the capacitor is halved 
C)  the capacitive reactance is halved 
D)  the power factor is doubled 
E)  the current amplitude is doubled 
A)  the impedance is doubled 
B)  the voltage across the capacitor is halved 
C)  the capacitive reactance is halved 
D)  the power factor is doubled 
E)  the current amplitude is doubled

Question 11

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 current 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 12

In a series RLC circuit the rms value of the generator emf is and the rms value of the current is i. The current lags the emf by $\phi$. The average power supplied by the generator is given by:

Accepted Answer

A)  (i/2)cos $\phi$ 
B)  i 
C)  i2/Z 
D)  i2Z 
E)  i2R 
A)  (i/2)cos $\phi$ 
B)  i 
C)  i2/Z 
D)  i2Z 
E)  i2R

Question 13

The units of the power factor are:

Accepted Answer

A)  ohm 
B)  watt 
C)  radian 
D)  ohm1/2 
E)  none of these 
A)  ohm 
B)  watt 
C)  radian 
D)  ohm1/2 
E)  none of these

Question 14

A 45-mH inductor is connected to an ac source of emf with a frequency of 400 Hz and a maximum emf of 20 V. The maximum current is:

Accepted Answer

A)  0 A 
B)  0.18 A 
C)  1.1 A 
D)  360 A 
E)  2300 A 
A)  0 A 
B)  0.18 A 
C)  1.1 A 
D)  360 A 
E)  2300 A

Question 15

In an RLC series circuit, the source voltage is leading the current at a given frequency f. If f is lowered slightly, then the circuit impedance will:

Accepted Answer

A)  increase 
B)  decrease 
C)  remain the same 
D)  cannot answer without knowing the amplitude of the source voltage 
E)  cannot answer without knowing whether the phase angle is larger or smaller than 45$\degree$ 
A)  increase 
B)  decrease 
C)  remain the same 
D)  cannot answer without knowing the amplitude of the source voltage 
E)  cannot answer without knowing whether the phase angle is larger or smaller than 45$\degree$

Question 16

The ideal meters shown read rms current and voltage. The average power delivered to the load is:

Accepted Answer

A)  definitely not equal to VI 
B)  perhaps more than VI 
C)  possibly equal to VI even if the load contains an inductor and a capacitor 
D)  definitely less than VI 
E)  zero as is the average of any sine wave 
A)  definitely not equal to VI 
B)  perhaps more than VI 
C)  possibly equal to VI even if the load contains an inductor and a capacitor 
D)  definitely less than VI 
E)  zero as is the average of any sine wave

Question 17

An electric motor, under load, has an effective resistance of 30  $\Omega$  and an inductive reactance of 40  $\Omega$ . When powered by a source with a maximum voltage of 420 V, the maximum current is:

Accepted Answer

A)  6.0 A 
B)  8.4 A 
C)  10.5 A 
D)  12 A 
E)  14 A 
A)  6.0 A 
B)  8.4 A 
C)  10.5 A 
D)  12 A 
E)  14 A

Question 18

The rapid exponential decay in just a few cycles of the charge on the plates of capacitor in an RLC circuit might due to:

Accepted Answer

A)  a large inductance 
B)  a large capacitance 
C)  a small capacitance 
D)  a large resistance 
E)  a small resistance 
A)  a large inductance 
B)  a large capacitance 
C)  a small capacitance 
D)  a large resistance 
E)  a small resistance

Question 19

In the circuit shown, switch S is first pushed up to charge the capacitor. When S is then pushed down, the current in the circuit will oscillate at a frequency of:

Accepted Answer

A)  0.010 Hz 
B)  12.5 Hz 
C)  320 Hz 
D)  2000 Hz 
E)  depends on V0 
A)  0.010 Hz 
B)  12.5 Hz 
C)  320 Hz 
D)  2000 Hz 
E)  depends on V0

Question 20

The angular frequency of a certain RLC series circuit is $ \omega $0. A source of sinusoidal emf, with angular frequency 2$ \omega $0, is inserted into the circuit. After transients die out the angular frequency of the current oscillations is:

Accepted Answer

A)  $ \omega $0/2 
B)  $ \omega $0 
C)  1.5$ \omega $0  
D)  2$ \omega $0 
E)  3$ \omega $0 
A)  $ \omega $0/2 
B)  $ \omega $0 
C)  1.5$ \omega $0  
D)  2$ \omega $0 
E)  3$ \omega $0

Exam 31: Electromagnetic Oscillations and Alternating Current

When the frequency of the oscillator in a series RLC circuit is doubled:

The total energy in an LC circuit is 5.0 *10-6 J. If C = 15 μ\muμ F the maximum charge on the capacitor is:

In a sinusoidally driven series RLC circuit the current lags the applied emf. The rate at which energy is dissipated in the resistor can be increased by:

An LC circuit has a capacitance of 30 μ\muμ F and an inductance of 15 mH. At time t = 0 the charge on the capacitor is 10 μ\muμ C and the current is 20 mA. The maximum charge on the capacitor is:

A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 μ\muμ J. At a certain instant the energy in the capacitor is 40 μ\muμ J. At that instant what is the emf induced in the inductor?

A coil has a resistance of 60 Ω\OmegaΩ and an impedance of 100 Ω\OmegaΩ . Its reactance is:

The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. If R is connected directly to the source it will dissipate a power of:

The impedance of an RLC series circuit is definitely increased if:

In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is:

When the amplitude of the oscillator in a series RLC circuit is doubled:

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 current is a maximum is:

In a series RLC circuit the rms value of the generator emf is and the rms value of the current is i. The current lags the emf by ϕ\phiϕ . The average power supplied by the generator is given by:

The units of the power factor are:

A 45-mH inductor is connected to an ac source of emf with a frequency of 400 Hz and a maximum emf of 20 V. The maximum current is:

In an RLC series circuit, the source voltage is leading the current at a given frequency f. If f is lowered slightly, then the circuit impedance will:

The ideal meters shown read rms current and voltage. The average power delivered to the load is:

An electric motor, under load, has an effective resistance of 30 Ω\OmegaΩ and an inductive reactance of 40 Ω\OmegaΩ . When powered by a source with a maximum voltage of 420 V, the maximum current is:

The rapid exponential decay in just a few cycles of the charge on the plates of capacitor in an RLC circuit might due to:

In the circuit shown, switch S is first pushed up to charge the capacitor. When S is then pushed down, the current in the circuit will oscillate at a frequency of:

The angular frequency of a certain RLC series circuit is ω \omega ω 0. A source of sinusoidal emf, with angular frequency 2 ω \omega ω 0, is inserted into the circuit. After transients die out the angular frequency of the current oscillations is:

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The total energy in an LC circuit is 5.0 *10^-6 J. If C = 15 $\mu$ F the maximum charge on the capacitor is:

An LC circuit has a capacitance of 30 $\mu$ F and an inductance of 15 mH. At time t = 0 the charge on the capacitor is 10 $\mu$ C and the current is 20 mA. The maximum charge on the capacitor is:

A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 $\mu$ J. At a certain instant the energy in the capacitor is 40 $\mu$ J. At that instant what is the emf induced in the inductor?

A coil has a resistance of 60 $\Omega$ and an impedance of 100 $\Omega$ . Its reactance is:

In a series RLC circuit the rms value of the generator emf is and the rms value of the current is i. The current lags the emf by $\phi$ . The average power supplied by the generator is given by:

An electric motor, under load, has an effective resistance of 30 $\Omega$ and an inductive reactance of 40 $\Omega$ . When powered by a source with a maximum voltage of 420 V, the maximum current is:

The angular frequency of a certain RLC series circuit is $\omega$ ₀. A source of sinusoidal emf, with angular frequency 2 $\omega$ ₀, is inserted into the circuit. After transients die out the angular frequency of the current oscillations is: