Question 1

The total energy in an LC circuit is 5.0 *10-6 J. If L = 25 mH the maximum current is:

Accepted Answer

A)  10 mA 
B)  14 mA 
C)  20 mA 
D)  28 mA 
E)  40 mA 
A)  10 mA 
B)  14 mA 
C)  20 mA 
D)  28 mA 
E)  40 mA

Question 2

In a sinusoidally driven series RLC circuit, the inductive resistance is XL = 200 $\Omega$, the capacitive reactance is XC = 100 $\Omega$, and the resistance is R = 50  $\Omega$. The current and applied emf would be in phase if:

Accepted Answer

A)  the resistance is increased to 100  $\Omega$, with no other changes 
B)  the resistance is increased to 200 $\Omega$, with no other changes 
C)  the inductance is reduced to zero, with no other changes 
D)  the capacitance is doubled, with no other changes 
E)  the capacitance is halved, with no other changes 
A)  the resistance is increased to 100  $\Omega$, with no other changes 
B)  the resistance is increased to 200 $\Omega$, with no other changes 
C)  the inductance is reduced to zero, with no other changes 
D)  the capacitance is doubled, with no other changes 
E)  the capacitance is halved, with no other changes

Question 3

An LC circuit has an oscillation frequency of 105 Hz. If C = 0.1 $\mu$F, then L must be about:

Accepted Answer

A)  10 mH 
B)  1 mH 
C)  25 $\mu$H 
D)  2.5 $\mu$H 
E)  1 pH 
A)  10 mH 
B)  1 mH 
C)  25 $\mu$H 
D)  2.5 $\mu$H 
E)  1 pH

Question 4

An RC series circuit is connected to an emf source having angular frequency   $ \omega $. The current:

Accepted Answer

A)  leads the source emf by tan-1(1/  $ \omega $CR) 
B)  lags the source emf by tan-1(1/  $ \omega $CR) 
C)  leads the source emf by tan-1(  $ \omega $CR) 
D)  lags the source emf by tan-1(  $ \omega $CR) 
E)  leads the source emf by  $\pi$/4 
A)  leads the source emf by tan-1(1/  $ \omega $CR) 
B)  lags the source emf by tan-1(1/  $ \omega $CR) 
C)  leads the source emf by tan-1(  $ \omega $CR) 
D)  lags the source emf by tan-1(  $ \omega $CR) 
E)  leads the source emf by  $\pi$/4

Question 5

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  $\Omega$ 
B)  0.25  $\Omega$ 
C)  4.0  $\Omega$ 
D)  20  $\Omega$ 
E)  100 $\Omega$ 
A)  0  $\Omega$ 
B)  0.25  $\Omega$ 
C)  4.0  $\Omega$ 
D)  20  $\Omega$ 
E)  100 $\Omega$

Question 6

In an RLC series circuit, which is connected to a source of emf mcos($ \omega $t), the current lags the voltage by 45$\degree$ if:

Accepted Answer

A)  R = 1/$ \omega $C - $ \omega $L 
B)  R = 1/$ \omega $L - $ \omega $C 
C)  R = $ \omega $L - 1/$ \omega $C 
D)  R = $ \omega $C - 1/$ \omega $L 
E)  $ \omega $L = 1/$ \omega $C 
A)  R = 1/$ \omega $C - $ \omega $L 
B)  R = 1/$ \omega $L - $ \omega $C 
C)  R = $ \omega $L - 1/$ \omega $C 
D)  R = $ \omega $C - 1/$ \omega $L 
E)  $ \omega $L = 1/$ \omega $C

Question 7

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)  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 8

In a purely inductive circuit, the current lags the voltage by:

Accepted Answer

A)  0 (they are in phase) 
B)  one-fourth of a cycle 
C)  one-half of a cycle 
D)  three-fourths of a cycle 
E)  one cycle 
A)  0 (they are in phase) 
B)  one-fourth of a cycle 
C)  one-half of a cycle 
D)  three-fourths of a cycle 
E)  one cycle

Question 9

The core of a transformer is made in a laminated form to:

Accepted Answer

A)  facilitate easy assembly 
B)  reduce i2R losses in the coils 
C)  increase the magnetic flux 
D)  save weight 
E)  prevent eddy currents 
A)  facilitate easy assembly 
B)  reduce i2R losses in the coils 
C)  increase the magnetic flux 
D)  save weight 
E)  prevent eddy currents

Question 10

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 current is:

Accepted Answer

A)  15 mA 
B)  20 mA 
C)  25 mA 
D)  35 mA 
E)  42 mA 
A)  15 mA 
B)  20 mA 
C)  25 mA 
D)  35 mA 
E)  42 mA

Question 11

An RLC series circuit has L = 100 mH and C = 1 $\mu$F. It is connected to a 1000-Hz source emf, and the voltage is found to lead the current by 75 $\degree$. The value of R is:

Accepted Answer

A)  12.6  $\Omega$ 
B)  126  $\Omega$ 
C)  175  $\Omega$ 
D)  1750  $\Omega$ 
E)  1810  $\Omega$ 
A)  12.6  $\Omega$ 
B)  126  $\Omega$ 
C)  175  $\Omega$ 
D)  1750  $\Omega$ 
E)  1810  $\Omega$

Question 12

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 inductor 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 13

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 A/s 
B)  1.7 *10-7 A/s 
C)  5.9 *10-3 A/s 
D)  3.8 * 10-2 A/s 
E)  170 A/s 
A)  0 A/s 
B)  1.7 *10-7 A/s 
C)  5.9 *10-3 A/s 
D)  3.8 * 10-2 A/s 
E)  170 A/s

Question 14

In a purely capacitive circuit the current:

Accepted Answer

A)  leads the voltage by one-fourth of a cycle 
B)  leads the voltage by one-half of a cycle 
C)  lags the voltage by one-fourth of a cycle 
D)  lags the voltage by one-half of a cycle 
E)  is in phase with the potential difference across the plates 
A)  leads the voltage by one-fourth of a cycle 
B)  leads the voltage by one-half of a cycle 
C)  lags the voltage by one-fourth of a cycle 
D)  lags the voltage by one-half of a cycle 
E)  is in phase with the potential difference across the plates

Question 15

A 35-$\mu$F capacitor is connected to an ac source of emf with a frequency of 250 Hz and a maximum emf of 20 V. If the voltage across the capacitor is zero at time t = 0, what is the voltage at time t = 3.0 ms? Assume the phase constant is zero.

Accepted Answer

A)  −20 V 
B)  −10 V 
C)  0 V 
D)  10 V 
E)  20 V 
A)  −20 V 
B)  −10 V 
C)  0 V 
D)  10 V 
E)  20 V

Question 16

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)  0.65 
E)  1.0 
A)  0 
B)  0.20 
C)  0.45 
D)  0.65 
E)  1.0

Question 17

For a power transmission line, the transmission should be at low current and high voltage because:

Accepted Answer

A)  this is the least dangerous to electrical workers 
B)  this gives the least dose of electromagnetic radiation to the public 
C)  this minimizes transmission losses 
D)  low current and high voltage is easier to transform than high current and low voltage 
E)  household appliances run at low current and high voltage 
A)  this is the least dangerous to electrical workers 
B)  this gives the least dose of electromagnetic radiation to the public 
C)  this minimizes transmission losses 
D)  low current and high voltage is easier to transform than high current and low voltage 
E)  household appliances run at low current and high voltage

Question 18

A series RL circuit is connected to an emf source of angular frequency  $ \omega $. The current:

Accepted Answer

A)  leads the applied emf by tan-1( $ \omega $L/R) 
B)  lags the applied emf by tan-1( $ \omega $L/R) 
C)  lags the applied emf by tan-1( $ \omega $R/L) 
D)  leads the applied emf by tan-1( $ \omega $R/L) 
E)  is zero 
A)  leads the applied emf by tan-1( $ \omega $L/R) 
B)  lags the applied emf by tan-1( $ \omega $L/R) 
C)  lags the applied emf by tan-1( $ \omega $R/L) 
D)  leads the applied emf by tan-1( $ \omega $R/L) 
E)  is zero

Question 19

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 20

An RLC circuit has a capacitance of 12 $\mu$F, an inductance of 25 mH, and a resistance of 60  $\Omega$. The current oscillates with an angular frequency of:

Accepted Answer

A)  1.2 *103 rad/s 
B)  1.4 * 103 rad/s 
C)  1.8 * 103 rad/s 
D)  2.2 *103 rad/s 
E)  2.6 * 103 rad/s 
A)  1.2 *103 rad/s 
B)  1.4 * 103 rad/s 
C)  1.8 * 103 rad/s 
D)  2.2 *103 rad/s 
E)  2.6 * 103 rad/s

Exam 31: Electromagnetic Oscillations and Alternating Current

The total energy in an LC circuit is 5.0 *10-6 J. If L = 25 mH the maximum current is:

In a sinusoidally driven series RLC circuit, the inductive resistance is XL = 200 Ω\OmegaΩ , the capacitive reactance is XC = 100 Ω\OmegaΩ , and the resistance is R = 50 Ω\OmegaΩ . The current and applied emf would be in phase if:

An LC circuit has an oscillation frequency of 105 Hz. If C = 0.1 μ\muμ F, then L must be about:

An RC series circuit is connected to an emf source having angular frequency ω \omega ω . The current:

A source with an impedance of 100 Ω\OmegaΩ 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 =

In an RLC series circuit, which is connected to a source of emf mcos( ω \omega ω t), the current lags the voltage by 45 °\degree° if:

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?

In a purely inductive circuit, the current lags the voltage by:

The core of a transformer is made in a laminated form 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 current is:

An RLC series circuit has L = 100 mH and C = 1 μ\muμ F. It is connected to a 1000-Hz source emf, and the voltage is found to lead the current by 75 °\degree° . The value of R 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 across the inductor 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:

In a purely capacitive circuit the current:

A 35- μ\muμ F capacitor is connected to an ac source of emf with a frequency of 250 Hz and a maximum emf of 20 V. If the voltage across the capacitor is zero at time t = 0, what is the voltage at time t = 3.0 ms? Assume the phase constant is zero.

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:

For a power transmission line, the transmission should be at low current and high voltage because:

A series RL circuit is connected to an emf source of angular frequency ω \omega ω . The current:

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

An RLC circuit has a capacitance of 12 μ\muμ F, an inductance of 25 mH, and a resistance of 60 Ω\OmegaΩ . The current oscillates with an angular frequency of:

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The total energy in an LC circuit is 5.0 *10^-6 J. If L = 25 mH the maximum current is:

In a sinusoidally driven series RLC circuit, the inductive resistance is X_L = 200 $\Omega$ , the capacitive reactance is X_C = 100 $\Omega$ , and the resistance is R = 50 $\Omega$ . The current and applied emf would be in phase if:

An LC circuit has an oscillation frequency of 10⁵ Hz. If C = 0.1 $\mu$ F, then L must be about:

An RC series circuit is connected to an emf source having angular frequency $\omega$ . The current:

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 =

In an RLC series circuit, which is connected to a source of emf _mcos( $\omega$ t), the current lags the voltage by 45 $\degree$ if:

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?

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 current is:

An RLC series circuit has L = 100 mH and C = 1 $\mu$ F. It is connected to a 1000-Hz source emf, and the voltage is found to lead the current by 75 $\degree$ . The value of R 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 inductor is:

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 35- $\mu$ F capacitor is connected to an ac source of emf with a frequency of 250 Hz and a maximum emf of 20 V. If the voltage across the capacitor is zero at time t = 0, what is the voltage at time t = 3.0 ms? Assume the phase constant is zero.

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:

A series RL circuit is connected to an emf source of angular frequency $\omega$ . The current:

An RLC circuit has a capacitance of 12 $\mu$ F, an inductance of 25 mH, and a resistance of 60 $\Omega$ . The current oscillates with an angular frequency of: