Question 1

A sinusoidal voltage V(t) has an rms value of 100 V. Its maximum value is:

Accepted Answer

A)  100 V 
B)  707 V 
C)  70.7 V 
D)  141 V 
E)  200 V 
A)  100 V 
B)  707 V 
C)  70.7 V 
D)  141 V 
E)  200 V

Question 2

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 3

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 4

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 
B)  T/4 
C)  T/2 
D)  T/1 
E)  2T 
A)  T 
B)  T/4 
C)  T/2 
D)  T/1 
E)  2T

Question 5

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)  0.38 A 
B)  0.025 A 
C)  40 A 
D)  2.3 A 
E)  5.3 A 
A)  0.38 A 
B)  0.025 A 
C)  40 A 
D)  2.3 A 
E)  5.3 A

Question 6

Which of the following has the greatest effect in decreasing the oscillation frequency of an LC circuit? Using instead:

Accepted Answer

A)  L/2 and C/2 
B)  L/2 and 2C 
C)  2L and C/2 
D)  2L and 2C 
E)  none of these 
A)  L/2 and C/2 
B)  L/2 and 2C 
C)  2L and C/2 
D)  2L and 2C 
E)  none of these

Question 7

A series circuit consists of a 15-$\Omega$resistor, a 25-mH inductor, and a 35-$\mu$F capacitor. If the frequency is 100 Hz the power factor is:

Accepted Answer

A)  0 
B)  0.20 
C)  0.45 
D)  0.40 
E)  1.0 
A)  0 
B)  0.20 
C)  0.45 
D)  0.40 
E)  1.0

Question 8

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

Question 9

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

Question 10

In the diagram, the function y(t) = ymsin($ \omega $t) is plotted as a solid curve. The other three curves have the form y(t) = ymsin($ \omega $t + $\phi$ ), where $\phi$  is between - $\pi$/2 and + $\pi$/2. Rank the curves according to the value of $\phi$  , from the most negative to the most positive.

Accepted Answer

A)  1, 2, 3 
B)  2, 3, 1 
C)  3, 2, 1 
D)  1, 3, 2 
E)  2, 1, 3 
A)  1, 2, 3 
B)  2, 3, 1 
C)  3, 2, 1 
D)  1, 3, 2 
E)  2, 1, 3

Question 11

In a series RLC circuit the rms value of the generator emf is E 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)  (iE/2)cos $\phi$ 
B)  iE 
C)  i2/Z 
D)  i2Z 
E)  i2R 
A)  (iE/2)cos $\phi$ 
B)  iE 
C)  i2/Z 
D)  i2Z 
E)  i2R

Question 12

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 13

A source with an impedance of 100 $\Omega$  is connected to the primary coil of a transformer and a resistance R is connected to the secondary coil. If the transformer has 500 turns in its primary coil and 100 turns in its secondary coil the greatest power will be dissipated in the resistor if R =:

Accepted Answer

A)  0 
B)  0.25$\Omega$ 
C)  4.0 $\Omega$ 
D)  50 $\Omega$ 
E)  100 $\Omega$ 
A)  0 
B)  0.25$\Omega$ 
C)  4.0 $\Omega$ 
D)  50 $\Omega$ 
E)  100 $\Omega$

Question 14

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.

Question 15

In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q. When the charge on the capacitor is Q/2, the energy stored in the inductor is:

Accepted Answer

A)  U/2 
B)  U/4 
C)  (4/3)U 
D)  3U/2 
E)  3U/4 
A)  U/2 
B)  U/4 
C)  (4/3)U 
D)  3U/2 
E)  3U/4

Question 16

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 17

An LC circuit has an inductance of 15 mH and a capacitance of 10 $\mu$F. At one instant the charge on the capacitor is 25 $\mu$C. At that instant the current is changing at the rate:

Accepted Answer

A)  0 
B)  1.7 * 10-8 A/s 
C)  5.9 * 10-3 A/s 
D)  3.8 *10-2 A/s 
E)  170 A/s 
A)  0 
B)  1.7 * 10-8 A/s 
C)  5.9 * 10-3 A/s 
D)  3.8 *10-2 A/s 
E)  170 A/s

Question 18

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)  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

Question 19

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 20

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/ $\pi$

Exam 31: Electromagnetic Oscillations and Alternating Current

A sinusoidal voltage V(t) has an rms value of 100 V. Its maximum value 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:

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

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:

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:

Which of the following has the greatest effect in decreasing the oscillation frequency of an LC circuit? Using instead:

A series circuit consists of a 15- Ω\OmegaΩ resistor, a 25-mH inductor, and a 35- μ\muμ F capacitor. If the frequency is 100 Hz the power factor is:

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:

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

In a series RLC circuit the rms value of the generator emf is E 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:

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

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

In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q. When the charge on the capacitor is Q/2, the energy stored in the inductor is:

The electrical analog of a spring constant k is:

An LC circuit has an inductance of 15 mH and a capacitance of 10 μ\muμ F. At one instant the charge on the capacitor is 25 μ\muμ C. At that instant the current is changing at the rate:

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?

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:

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

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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 series circuit consists of a 15- $\Omega$ resistor, a 25-mH inductor, and a 35- $\mu$ F capacitor. If the frequency is 100 Hz the power factor is:

In a series RLC circuit the rms value of the generator emf is E 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 LC circuit has an inductance of 15 mH and a capacitance of 10 $\mu$ F. At one instant the charge on the capacitor is 25 $\mu$ C. At that instant the current is changing at the rate:

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?

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: