Question 1

A resistor, an inductor, and a capacitor are connected in parallel to a sinusoidal source of emf. Which of the following is true?

Accepted Answer

A)  The currents in all branches are in phase. 
B)  The potential differences across all branches are in phase. 
C)  The current in the capacitor branch leads the current in the inductor branch by 1/4 cycle 
D)  The potential difference across the capacitor branch leads the potential difference across the inductor branch by 1/4 cycle. 
E)  The current in the capacitor branch lags the current in the inductor branch by 1/4 cycle. 
A)  The currents in all branches are in phase. 
B)  The potential differences across all branches are in phase. 
C)  The current in the capacitor branch leads the current in the inductor branch by 1/4 cycle 
D)  The potential difference across the capacitor branch leads the potential difference across the inductor branch by 1/4 cycle. 
E)  The current in the capacitor branch lags the current in the inductor branch by 1/4 cycle. B

Question 2

A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is:

Accepted Answer

A)  1000 V 
B)  500 V 
C)  250 V 
D)  100 V 
E)  10 V 
A)  1000 V 
B)  500 V 
C)  250 V 
D)  100 V 
E)  10 V A

Question 3

The main reason that alternating current replaced direct current for general use is:

Accepted Answer

A)  ac generators do not need slip rings 
B)  ac voltages may be conveniently transformed 
C)  electric clocks do not work on dc 
D)  a given ac current does not heat a power line as much as the same dc current 
E)  ac minimizes magnetic effects 
A)  ac generators do not need slip rings 
B)  ac voltages may be conveniently transformed 
C)  electric clocks do not work on dc 
D)  a given ac current does not heat a power line as much as the same dc current 
E)  ac minimizes magnetic effects B

Question 4

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 5

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 6

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 (in volts) across the inductor is:

Accepted Answer

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

Question 7

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

Accepted Answer

A)  40 
B)  60 
C)  80 
D)  117 
E)  160 
A)  40 
B)  60 
C)  80 
D)  117 
E)  160

Question 8

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 9

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 10

The rms value of a sinusoidal voltage is   , where V0 is the amplitude. What is the rms value of its fully rectified wave? Recall that Vrect(t) = $\mid$V(t)$\mid$.

Accepted Answer

A)    
B)    
C)    
D)    
E)    
A)    
B)    
C)    
D)    
E)

Question 11

An RLC circuit has an inductance of 25 mH and a capacitance of 5.0 $\mu$F. The charge on the capacitor does NOT oscillate but rather decays exponentially to zero. The resistance in the circuit must be:

Accepted Answer

A)  greater than or equal to 20,000 $\Omega$ 
B)  less than 20,000$\Omega$ but greater than 10,000 $\Omega$ 
C)  less than 10,000 $\Omega$ but greater than 5,000 $\Omega$ 
D)  less than 5,000 $\Omega$ but greater than 0 
E)  0 
A)  greater than or equal to 20,000 $\Omega$ 
B)  less than 20,000$\Omega$ but greater than 10,000 $\Omega$ 
C)  less than 10,000 $\Omega$ but greater than 5,000 $\Omega$ 
D)  less than 5,000 $\Omega$ but greater than 0 
E)  0

Question 12

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 13

The angular frequency of a certain RLC series circuit is  $ \omega $0. A source of sinusoidal emf, with angular frequency 2 $ \omega $, 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)  2 $ \omega $0 
D)  1.5 $ \omega $0 
E)  3 $ \omega $0 
A)   $ \omega $0/2 
B)   $ \omega $0 
C)  2 $ \omega $0 
D)  1.5 $ \omega $0 
E)  3 $ \omega $0

Question 14

An RLC series circuit is driven by a sinusoidal emf with angular frequency  $ \omega $d. If  $ \omega $d is increased without changing the amplitude of the emf the current amplitude increases. If the L is inductance, C is the capacitance, and R is the resistance, this means that:

Accepted Answer

A) $ \omega $dL > 1/ $ \omega $dC B) $ \omega $dL dC C) $ \omega $dL = 1/ $ \omega $dC D) $ \omega $dL > R E) $ \omega $dL < R A) $ \omega $dL > 1/ $ \omega $dC B) $ \omega $dL dC C) $ \omega $dL = 1/ $ \omega $dC D) $ \omega $dL > R E) $ \omega $dL < R

Question 15

The resistance of the primary coil of a well designed, 1:10 step-down transformer is 1 $\Omega$. With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:

Accepted Answer

A)  essentially zero 
B)  about 12 A 
C)  about 120 A 
D)  depends on the actual number of turns in the primary coil 
E)  depends on the core material 
A)  essentially zero 
B)  about 12 A 
C)  about 120 A 
D)  depends on the actual number of turns in the primary coil 
E)  depends on the core material

Question 16

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)  100 $\mu$F 
E)  1 pF 
A)  1 F 
B)  1 mF 
C)  1 $\mu$F 
D)  100 $\mu$F 
E)  1 pF

Question 17

An RLC circuit has a sinusoidal source of emf. The average rate at which the source supplies energy is 5 nW. This must also be:

Accepted Answer

A)  the average rate at which energy is stored in the capacitor 
B)  the average rate which energy is stored in the inductor 
C)  the average rate at which energy is dissipated in the resistor 
D)  twice the average rate at which energy is stored in the capacitor 
E)  three times the average rate at which energy is stored in the inductor 
A)  the average rate at which energy is stored in the capacitor 
B)  the average rate which energy is stored in the inductor 
C)  the average rate at which energy is dissipated in the resistor 
D)  twice the average rate at which energy is stored in the capacitor 
E)  three times the average rate at which energy is stored in the inductor

Question 18

In an oscillating LC circuit, the total stored energy is U. The maximum energy stored in the capacitor during one cycle is:

Accepted Answer

A)  U/2 
B)    
C)  U 
D)  U/(2 $\pi$) 
E)  U/ $\pi$ 
A)  U/2 
B)    
C)  U 
D)  U/(2 $\pi$) 
E)  U/ $\pi$

Question 19

An LC circuit consists of a 1 $\mu$F capacitor and a 4 mH inductor. Its oscillation frequency is approximately:

Accepted Answer

A)  0.025 Hz 
B)  25 Hz 
C)  60 Hz 
D)  2500 Hz 
E)  15,800 Hz 
A)  0.025 Hz 
B)  25 Hz 
C)  60 Hz 
D)  2500 Hz 
E)  15,800 Hz

Question 20

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 potential difference across the capacitor?

Accepted Answer

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

Exam 31: Electromagnetic Oscillations and Alternating Current

A resistor, an inductor, and a capacitor are connected in parallel to a sinusoidal source of emf. Which of the following is true?

A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is:

The main reason that alternating current replaced direct current for general use 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:

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:

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 (in volts) across the inductor is:

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

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

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:

The rms value of a sinusoidal voltage is , where V0 is the amplitude. What is the rms value of its fully rectified wave? Recall that Vrect(t) = ∣\mid∣ V(t) ∣\mid∣ .

An RLC circuit has an inductance of 25 mH and a capacitance of 5.0 μ\muμ F. The charge on the capacitor does NOT oscillate but rather decays exponentially to zero. The resistance in the circuit must be:

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 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 , is inserted into the circuit. After transients die out the angular frequency of the current oscillations is:

An RLC series circuit is driven by a sinusoidal emf with angular frequency ω \omega ω d. If ω \omega ω d is increased without changing the amplitude of the emf the current amplitude increases. If the L is inductance, C is the capacitance, and R is the resistance, this means that:

The resistance of the primary coil of a well designed, 1:10 step-down transformer is 1 Ω\OmegaΩ . With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:

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:

An RLC circuit has a sinusoidal source of emf. The average rate at which the source supplies energy is 5 nW. This must also be:

In an oscillating LC circuit, the total stored energy is U. The maximum energy stored in the capacitor during one cycle is:

An LC circuit consists of a 1 μ\muμ F capacitor and a 4 mH inductor. Its oscillation frequency is approximately:

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 potential difference across the capacitor?

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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:

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 (in volts) across the inductor is:

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

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 circuit has an inductance of 25 mH and a capacitance of 5.0 $\mu$ F. The charge on the capacitor does NOT oscillate but rather decays exponentially to zero. The resistance in the circuit must be:

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

An RLC series circuit is driven by a sinusoidal emf with angular frequency $\omega$ _d. If $\omega$ _d is increased without changing the amplitude of the emf the current amplitude increases. If the L is inductance, C is the capacitance, and R is the resistance, this means that:

The resistance of the primary coil of a well designed, 1:10 step-down transformer is 1 $\Omega$ . With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:

An LC circuit consists of a 1 $\mu$ F capacitor and a 4 mH inductor. Its oscillation frequency is approximately:

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 potential difference across the capacitor?