Question 1

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 E

Question 2

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 D

Question 3

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 C

Question 4

The average power supplied to the circuit shown passes through a maximum when which one of the following is increased continuously from a very low to a very high value?

Accepted Answer

A) source emf 
B) R 
C) C 
D) source frequency f 
E) none of these 
A) source emf 
B) R 
C) C 
D) source frequency f 
E) none of these

Question 5

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  $ \omega $/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  $ \omega $/4

Question 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

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 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 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 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

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 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) 16,000 Hz 
A) 0.025 Hz 
B) 25 Hz 
C) 60 Hz 
D) 2500 Hz 
E) 16,000 Hz

Question 20

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

Exam 31: Electromagnetic Oscillations and Alternating Current

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

A step-down transformer is used to:

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:

The average power supplied to the circuit shown passes through a maximum when which one of the following is increased continuously from a very low to a very high value?

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

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

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 =

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

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

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 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 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:

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:

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

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

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

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Filters

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

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

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 =

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

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:

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