Download EM Oscillations and Alternating Curent

Q1) A charged capacitor and an inductor are connected in series. At time t
= 0 s, the current is zero and the capacitor is fully charged. If T is the
period of the resulting oscillations, the first time after t = 0 that (a) the
charge on the capacitor is a maximum and (b) the energy stored in the
magnetic field of the inductor is a maximum is
1) (a) T
2) (a) T
3) (a) T/2
4) (a) T/2
5) (a) T/4
(b) T/4
(b) T/2
(b) T/4
(b) T/2
(b) T
Q2) A charged capacitor and an inductor are connected in series. At time
t = 0 s, the current is zero and the capacitor is fully charged. If T is the
period of the resulting oscillations, the first time after t = 0 that (a) the
voltage across the capacitor is a maximum (with its initial polarity) and
(b) the current is a maximum is
1) (a) T
2) (a) T
3) (a) T/2
4) (a) T/2
5) (a) T/4
(b) T/4
(b) T/2
(b) T/4
(b) T/2
(b) T
Q3) The figure below shows three oscillating LC circuits with
identical inductors and capacitors. Rank the circuits according to
the time taken to fully discharge the capacitors during the
oscillations, greatest first.
1) a, b, c
2) a, c, b
3) b, c, a
4) b, a, c
5) c, a, b
Q4) For each of the curves of q(t) in the figure below for an LC
circuit, determine the least positive phase constant  in the
equation q  Q cos( t  ) required to produce the curve.
1) (a) 3(b) (c) 
2) (a) 3(b) (c) 
3) (a) (b) (c) 3
4) (a) (b) 3(c) 
5) (a) (b) (c) 3
Q5) Which of the following has the greatest effect in decreasing
the oscillation frequency of an LC circuit? Using instead:
1) L/2 and C/2
2) L/2 and 2C
3) 2L and C/2
4) 2L and 2C
5) none of these
Q6) 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:
1) U/2
2) U/4
3) (4/3)U
4) 3U/2
5) 3U/4
Q7) The figure below shows graphs of the capacitor voltage vC for LC
circuits 1 and 2, which contain identical capacitances and have the same
maximum charge Q. Are (a) the inductance and (b) the maximum current I
in circuit 1 greater than, less than, or the same as those in circuit 2?
1) (a) greater than
2) (a) greater than
3) (a) less than
4) (a) less than
(b) greater than
(b) less than
(b) greater than
(b) less than
Q8) Which one of the following graphs illustrates how capacitive
reactance varies with frequency?
Q9) Which one of the following graphs shows how the inductive
reactance varies with frequency?
Q10) For a capacitor in an ac circuit, how much energy is stored in
the capacitor at the instant when current is zero?
1) zero
2) maximum
3) half of the maximum amount
4) impossible to tell without the phase angle
Q11) An alternating emf source is connected, in turn, to a resistor, a
capacitor, and then an inductor. Once connected to these devices, the
driving frequency fd is varied and the amplitude I of the resulting current
through the device is measured and plotted. Which of the three plots in the
figure below corresponds to which of the three devices?
1) (a) capacitor (b) resistor (c) inductor
2) (a) inductor (b) resistor (c) capacitor
3) (a) inductor (b) capacitor (c) resistor
4) none of the above
Q12) If we increase the driving frequency in a circuit with a purely
resistive load, do (a) VR and (b) IR increase, decrease, or remain the
same?
1)
2)
3)
4)
5)
(a) increase
(a) increase
(a) same
(a) same
(a) decrease
(b) increase
(b) same
(b) same
(b) increase
(b) decrease
Q13) If we increase the driving frequency in a circuit with a purely
capacitive load, do (a) Vc and (b) Ic increase, decrease, or remain
the same?
1)
2)
3)
4)
5)
(a) increase
(a) increase
(a) same
(a) same
(a) decrease
(b) increase
(b) same
(b) same
(b) increase
(b) decrease
Q14) If we increase the driving frequency in a circuit with a purely
inductive load, do (a) VL and (b) IL increase, decrease, or remain
the same?
1)
2)
3)
4)
5)
(a) increase
(a) increase
(a) same
(a) same
(a) same
(b) increase
(b) same
(b) same
(b) increase
(b) decrease
Q15) This graph shows the peak current as a function of frequency
for an unknown circuit element placed in the diagrammed circuit.
Line c represents the current through a(n)
1) capacitor.
2) inductor.
3) resistor.
4) impossible to say
Q16) This graph shows the peak current as a function of frequency
for an unknown circuit element placed in the diagrammed circuit.
Line a represents the current through a(n)
1) capacitor.
2) inductor.
3) resistor.
4) impossible to say.
Q17) The voltage across and the current
through a single circuit element connected
to an ac generator are shown in the graph.
Which one of the following statements
concerning this circuit element is true?
1) The element is a resistor.
2) The element is a capacitor.
3) The element is an inductor.
4) The element could be a resistor or an inductor.
5) The element could be an inductor or a capacitor.
Q18) The graph shows the voltage across and the current through a
single circuit element connected to an ac generator. Identify the
circuit element.
1) The element is a 25-Ω resistor.
2) The element is a 35-Ω resistor.
3) The element is a 0.45-H inductor.
4) The element is a 360-μF capacitor.
5) The element is a 510-μF capacitor.
Q19) The graph below shows the current and the voltage for a
capacitor connected to an ac power source. Which of the lines
represents the current?
1) line 1
2) line 2
3) this graph isn't correct for a capacitor.
Q20) The graph below shows the current and the voltage for an
inductor connected to an ac power source. Which of the lines
represents the current?
1) line 1
2) line 2
3) this graph isn't correct for an inductor
Q21) The graph below shows the current and the voltage for a
resistor connected to an ac power source. Which of the lines
represents the current?
1) line 1
2) line 2
3) this graph isn't correct for a resistor.
Q22) A capacitor and an inductor have the same reactance at a
certain frequency, o. Which of the following is true for
frequencies  > o?
1) XC > XL
2) XC < XL
3) XC = XL
4) Impossible to tell.
Q23) Does the phasor diagram shown in the figure below
correspond to an alternating emf source connected to a
resistor, a capacitor, or an inductor?
1) a resistor
2) a capacitor
3) an inductor
Q24) Figure (a) below shows, in a sine curve S(t) = sin(dt) and
three other sinusoidal curves A(t), B(t), and C(t), each of the form
sin(dt-). Which of the phasors shown in figure (b) corresponds
to the curve S(t)?
1) 1
2) 2
3) 3
4) 4
Q25) The phasor diagrams below represent three oscillating emfs
having different amplitudes and frequencies at a certain instant of
time t =0. As t increases, each phasor rotates counterclockwise and
completely determines a sinusoidal oscillation. At the instant of
time shown, the magnitude of E associated with each phasor
given in ascending order by diagrams
1) (a), (b), and (c).
2) (a), (c), and (b).
3) (b), (c), and (a).
4) (c), (a), and (b).
5) none of the above
Q26) Which one of the following phasor models correctly
represents a circuit comprised of only an inductor and an ac
generator?
Q27) Which of the following is the correct phasor representation
for an RLC circuit?
1) A
2) B
3) C
4) D
Q28) An ac power source is connected to a series combination of a
resistor, a capacitor, and an inductor. Which statement is correct?
1) The voltage across the capacitor leads the voltage across the
inductor by 180o.
2) The voltage across the capacitor lags the voltage across the
inductor by 180o.
3) The voltage across the capacitor and the inductor are in phase.
4) The voltage across the capacitor and the resistor are in phase.
Q29) The impedance of an RLC circuit is definitely
increased if:
1) C increases
2) L increases
3) R increases
4) two of the above
5) all of the above
Q30) Which one of the following statements concerning the impedance of
an RCL circuit is true?
1) The impedance is dominated by the capacitance at low frequencies.
2) The impedance is dominated by the resistance at high frequencies.
3) The impedance depends only on the values of C and L.
4) The impedance depends only on the resistance.
5) The impedance is independent of frequency.
Q31) The figure below shows the current i and driving
emf  for a series RLC circuit. Is the angular frequency d of
the emf greater than or less than the natural angular
frequency ?
1) greater than
2) less than
Q32) The figure below shows the current i and driving emf  for a
series RLC circuit. Relative to the emf curve, does the current
curve shift leftward or rightward if we slightly increase (a) L,
(b) C, and (c) d?
1) (a) right
2) (a) right
3) (a) right
4) (a) left
5) (a) left
(b) right
(b) left
(b) left
(b) left
(b) right
(c) right
(c) right
(c) left
(c) left
(c) left
Q33) 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:
1) decreasing the capacitance and making no other charges
2) increasing the capacitance and making no other charges
3) increasing the inductance and making no other charges
4) increasing the driving frequency and making no other charges
5) two of the above
Q34) An AC generator produces 10 V (rms) at 400 rad/s. It is
connected to a series RL circuit (R = 17.3 W, L = 0.025 H). The
rms current is:
1) 0.025 A and leads the emf by 60o
2) 0.025 A and lags the emf by 60o
3) 0.50 A and leads the emf by 30o
4) 0.50 A and lags the emf by 30o
5) 0.58 A and lags the emf by 30o
Q35) An RLC series circuit, connected to an alternating voltage
source, is at resonance. Then:
1) the voltage across R is zero
2) the voltage across R equals the applied voltage
3) the voltage across C is zero
4) the voltage across L equals the applied voltage
5) the applied voltage and current differ in phase by 90o
Q36) What is the resonant frequency for an RLC circuit consisting
of a 60.0 µF capacitor, a 15.0 mH inductor, and a 12.0 Ω resistor?
1) 1.05 kHz
2) 1.11 mHz
3) 0.949 mHz
4) 304 Hz
Q37) An RLC series circuit is driven by a sinusoidal emf with
angular frequency d. If d is increased without changing the
amplitude of the emf the current amplitude increases. If L is
the inductance, C is the capacitance, and R is the resistance, this
means that:
1) dL > 1/dC
2) dL < 1/dC
3) dL = 1/dC
4) dL > R
5) dL < R
Q38) The impedance of an RLC series circuit is definitely increased
if:
1) C decreases
2) L increases
3) L decreases
4) R increases
5) R decreases
Q39) The impedance of the circuit shown is:
1) 21 
2) 50 
3) 63 
4) 65 
5) 98 
Q40) Here are the capacitive reactance and inductive reactance,
respectively, for three sinusoidally driven series RLC circuits:
(1) 50 , 100 ;
(2) 100 , 50 ;
(3) 50 , 50 .
For which does the current lag the applied emf?
1) 1
2) 2
3) 3
4) none of them
Q41) Use the information given in the figure for the series RCL
circuit to determine its total impedance.
1) 300 Ω
2) 500 Ω
3) 1500 Ω
4) 1700 Ω
5) 1900 Ω
Q42) (a) If the current in a sinusoidally driven series RLC circuit
leads the emf, would we increase or decrease the capacitance to
increase the rate at which energy is supplied to the resistance? (b)
Will this change bring the resonant angular frequency of the circuit
closer to the angular frequency of the emf or put it farther away?
1)
2)
3)
4)
(a) increase
(a) increase
(a) decrease
(a) decrease
(b) closer
(b) farther
(b) closer
(b) farther
Q43) The table below shows the values of the resistance,
capacitive reactance, and inductive reactance for five RCL circuits.
Which circuit will have a negative phase angle?
1)
2)
3)
4)
5)
Resistance
78 Ω
86 Ω
120 Ω
127 Ω
148 Ω
Capacitive Reactance
306 Ω
49 Ω
314 Ω
218 Ω
219 Ω
Inductive Reactance
346 Ω
86 Ω
314 Ω
306 Ω
180 Ω
Q44) For the RLC series circuit shown, how
many of these statements is/are true:
 Potential energy oscillates between C and L.
 The source does no net work: Energy lost in R is compensated
by energy stored in C and L.
 The current through C is 90° out of phase with the one through L.
 The current through Cis 180° out of phase with the one
through L.
 All energy is dissipated in R.
Q45) The current in a certain ac circuit is independent of the
frequency at a given voltage. Which combination of elements is
most likely to comprise the circuit?
1) resistors only
2) inductors only
3) capacitors only
4) a combination of inductors and resistors
5) a combination of inductors and capacitors
Q46) 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:
1) 25,600 V
2) 3200 V
3) 400 V
4) 50 V
5) 6.25 V
Q47) When the switch is closed, the potential difference across R
is
1) VN2 /N1.
2) VN1/N2.
3) V.
4) zero.
5) insufficient information
H
Q48) The primary coil of a transformer is connected to a battery, a
resistor, and a switch. The secondary coil is connected to an
ammeter. When the switch is thrown closed, the ammeter shows
1) zero current.
2) a nonzero current for a
short instant.
3) a steady current.
Q49) An alternating-current emf device has a smaller resistance
than that of the resistive load; to increase the transfer of energy
from the device to the load, a transformer will be connected
between the two. (a) Should Ns be greater than or less than Np?
(b) Will that make it a step-up or step-down transformer?
1)
2)
3)
4)
(a) less than
(a) less than
(a) greater than
(a) greater than
(b) step-up
(b) step-down
(b) step-up
(b) step-down
Q50) 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:
1) decreasing the capacitance and making no other changes
2) increasing the capacitance and making no other changes
3) increasing the inductance and making no other changes
4) increasing the driving frequency and making no other changes
5) decreasing the amplitude of the driving emf and making no
other changes
Q51) The graphs show the total
electromagnetic energy in two RLC circuits as
functions of time. Which of the following
statements might be true?
1) Circuit 1 has a smaller resistance and a larger inductance
2) Circuit 1 has a larger resistance and a smaller inductance
3) Circuit 1 has the same resistance and a larger inductance
4) Circuit 1 has a larger resistance and a larger capacitance
5) Circuit 1 has the same resistance and a smaller capacitance
Q52) For which one of the following circuit arrangements will the
power factor be non-zero?
1) a capacitor in series with an ac generator
2) an inductor in series with an ac generator
3) two capacitors in series with an ac generator
4) a capacitor and resistor in series with an ac generator
5) a capacitor and inductor in series with an ac generator