Alternating Current- 2 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In a series LCR circuit capacitance is changed from C to 2
C. For the resonant frequency to remain unchanged, the
inductance would be changed from L to
(a) L/2 (b) 2 L (c) 4 L (d) L/4
Q.2 The power factor of 
LCR
circuit at resonance is
(a) 0.707 (b)1 (c) Zero (d) 0.5
Q.3 An alternating current source of frequency 100 Hz is
joined to a combination of a resistance, a capacitance and
a inductance in series. The potential difference across the
inductance, the resistance and the capacitor is 46, 8 and
40 volt respectively . The electromotive force of alternating
current source in volt is
(a) 94 (b) 14 (c) 10 (d) 76
Q.4 A 10 ohm resistance, 5 mH inductance coil and 10 mF
capacitor are joined in series. When a suitable frequency
alternating current source is joined to this combination,
the circuit resonates. If the resistance is halved, the
resonance frequency
(a) is halved (b) is doubled
(c) remains unchanged (d) is quadrupled
Q.5 The phase difference between the current and voltage of
LCR circuit in series combination at resonance is
(a) 0° (b) p/2
(c) p (d)–p
Page 2


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In a series LCR circuit capacitance is changed from C to 2
C. For the resonant frequency to remain unchanged, the
inductance would be changed from L to
(a) L/2 (b) 2 L (c) 4 L (d) L/4
Q.2 The power factor of 
LCR
circuit at resonance is
(a) 0.707 (b)1 (c) Zero (d) 0.5
Q.3 An alternating current source of frequency 100 Hz is
joined to a combination of a resistance, a capacitance and
a inductance in series. The potential difference across the
inductance, the resistance and the capacitor is 46, 8 and
40 volt respectively . The electromotive force of alternating
current source in volt is
(a) 94 (b) 14 (c) 10 (d) 76
Q.4 A 10 ohm resistance, 5 mH inductance coil and 10 mF
capacitor are joined in series. When a suitable frequency
alternating current source is joined to this combination,
the circuit resonates. If the resistance is halved, the
resonance frequency
(a) is halved (b) is doubled
(c) remains unchanged (d) is quadrupled
Q.5 The phase difference between the current and voltage of
LCR circuit in series combination at resonance is
(a) 0° (b) p/2
(c) p (d)–p
2
DPP/ P 47
Q.6 The coefficient of induction of a choke coil is 0.1H and
resistance is 12W. If it is connected to an alternating current
source of frequency 60 Hz, then power factor is
approximately
(a) 0.4 (b) 0.30 (c) 0.2 (d) 0.1
Q.7 The resonant frequency of a circuit is f. If the capacitance
is made 4 times the initial values, then the resonant
frequency will become
(a) f /2 (b) 2f (c)f (d) f/4
Q.8 In the non-resonant circuit, what will be the nature of the
circuit for frequencies higher than the resonant frequency?
(a) Resistive (b) Capacitive
(c) Inductive (d) None of the above
Q.9 In a series LCR circuit, resistance R = 10W and the impedance
Z = 20W . The phase difference between the current and the
voltage is
(a) 30° (b) 45° (c) 60° (d) 90°
Q.10An alternating e.m.f. of frequency 
1
2
æö
n=
ç÷
èø
p LC
is
applied to a series 
LCR
circuit. For this frequency of the
applied e.m.f.
(a) The circuit is at resonance and its impedance is made
up only of a reactive part
(b) The current in the circuit is not in phase with the
applied e.m.f. and the voltage across R equals this
applied emf
(c) The sum of the p.d.’s across the inductance and
capacitance equals the applied e.m.f. which is 180°
ahead of phase of the current in the circuit
(d) The quality factor of the circuit is 
/ LR w
or 
1/ CR w
and this is a measure of the voltage magnification
(produced by the circuit at resonance) as well as the
sharpness of resonance of the circuit
Q.11 In a circuit L,C and R are connected in series with an
alternating voltage source of frequency f. The current leads
the voltage by 45°. The value of C is
(a)
1
2(2) f fLR p p+
(b)
1
(2) f fLR p p+
(c)
1
2(2) f fLR p p-
(d)
1
(2) f fLR p p-
Q.12 For the series 
LCR
circuit shown in the figure, what is the
resonance frequency and the amplitude of the current at
the resonating frequency
220 V
8 mH
44 W
20µF
(a) 
1
2500rad s
-
 and 5 2A (b) 
1
2500rad s
-
 and 
5A
(c) 
1
2500rad s
-
 and 
5
A
2
(d) 
1
25rad s
-
 and    
5 2A
Q.13 In an ac circuit, V and I are given by 100sin(100 ) Vt = volt,
sin 100 mA
3
It
p æö
=+
ç÷
èø
. The average power dissipated in
circuit is
(a) 10
4
 watt (b) 10 watt
(c) 0.025 watt (d)   2.5 watt
Q.14 For a series LCR circuit R = X
L
 = 2X
C
. The impedance of
the circuit and phase difference between V and I
respectively will be
(a)
1
5R
,tan (2)
2
-
(b)
1
5R
,tan (1/ 2)
2
-
(c)
1
C
5X ,tan (2)
-
(d)
1
5R,tan (1/ 2)
-
Q.15 If a current  I given by 
0
I sin
2
t
p æö
w-
ç÷
èø
 flows in an ac circuit
across which an ac potential of 
0
sin EEt =w has been
applied, then the average power consumption P in the circuit
will be
(a) 
00
2
EI
P =
(b) 
00
2 P El =
(c) 
00
2
EI
P =
(d) 
0 P =
Q.16 An ac supply gives 
30V
r .m.s. which passes through a 10 W
resistance. The power dissipated in it is
(a) 902 W (b) 90 
W
(c) 452 W (d) 45 
W
Page 3


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In a series LCR circuit capacitance is changed from C to 2
C. For the resonant frequency to remain unchanged, the
inductance would be changed from L to
(a) L/2 (b) 2 L (c) 4 L (d) L/4
Q.2 The power factor of 
LCR
circuit at resonance is
(a) 0.707 (b)1 (c) Zero (d) 0.5
Q.3 An alternating current source of frequency 100 Hz is
joined to a combination of a resistance, a capacitance and
a inductance in series. The potential difference across the
inductance, the resistance and the capacitor is 46, 8 and
40 volt respectively . The electromotive force of alternating
current source in volt is
(a) 94 (b) 14 (c) 10 (d) 76
Q.4 A 10 ohm resistance, 5 mH inductance coil and 10 mF
capacitor are joined in series. When a suitable frequency
alternating current source is joined to this combination,
the circuit resonates. If the resistance is halved, the
resonance frequency
(a) is halved (b) is doubled
(c) remains unchanged (d) is quadrupled
Q.5 The phase difference between the current and voltage of
LCR circuit in series combination at resonance is
(a) 0° (b) p/2
(c) p (d)–p
2
DPP/ P 47
Q.6 The coefficient of induction of a choke coil is 0.1H and
resistance is 12W. If it is connected to an alternating current
source of frequency 60 Hz, then power factor is
approximately
(a) 0.4 (b) 0.30 (c) 0.2 (d) 0.1
Q.7 The resonant frequency of a circuit is f. If the capacitance
is made 4 times the initial values, then the resonant
frequency will become
(a) f /2 (b) 2f (c)f (d) f/4
Q.8 In the non-resonant circuit, what will be the nature of the
circuit for frequencies higher than the resonant frequency?
(a) Resistive (b) Capacitive
(c) Inductive (d) None of the above
Q.9 In a series LCR circuit, resistance R = 10W and the impedance
Z = 20W . The phase difference between the current and the
voltage is
(a) 30° (b) 45° (c) 60° (d) 90°
Q.10An alternating e.m.f. of frequency 
1
2
æö
n=
ç÷
èø
p LC
is
applied to a series 
LCR
circuit. For this frequency of the
applied e.m.f.
(a) The circuit is at resonance and its impedance is made
up only of a reactive part
(b) The current in the circuit is not in phase with the
applied e.m.f. and the voltage across R equals this
applied emf
(c) The sum of the p.d.’s across the inductance and
capacitance equals the applied e.m.f. which is 180°
ahead of phase of the current in the circuit
(d) The quality factor of the circuit is 
/ LR w
or 
1/ CR w
and this is a measure of the voltage magnification
(produced by the circuit at resonance) as well as the
sharpness of resonance of the circuit
Q.11 In a circuit L,C and R are connected in series with an
alternating voltage source of frequency f. The current leads
the voltage by 45°. The value of C is
(a)
1
2(2) f fLR p p+
(b)
1
(2) f fLR p p+
(c)
1
2(2) f fLR p p-
(d)
1
(2) f fLR p p-
Q.12 For the series 
LCR
circuit shown in the figure, what is the
resonance frequency and the amplitude of the current at
the resonating frequency
220 V
8 mH
44 W
20µF
(a) 
1
2500rad s
-
 and 5 2A (b) 
1
2500rad s
-
 and 
5A
(c) 
1
2500rad s
-
 and 
5
A
2
(d) 
1
25rad s
-
 and    
5 2A
Q.13 In an ac circuit, V and I are given by 100sin(100 ) Vt = volt,
sin 100 mA
3
It
p æö
=+
ç÷
èø
. The average power dissipated in
circuit is
(a) 10
4
 watt (b) 10 watt
(c) 0.025 watt (d)   2.5 watt
Q.14 For a series LCR circuit R = X
L
 = 2X
C
. The impedance of
the circuit and phase difference between V and I
respectively will be
(a)
1
5R
,tan (2)
2
-
(b)
1
5R
,tan (1/ 2)
2
-
(c)
1
C
5X ,tan (2)
-
(d)
1
5R,tan (1/ 2)
-
Q.15 If a current  I given by 
0
I sin
2
t
p æö
w-
ç÷
èø
 flows in an ac circuit
across which an ac potential of 
0
sin EEt =w has been
applied, then the average power consumption P in the circuit
will be
(a) 
00
2
EI
P =
(b) 
00
2 P El =
(c) 
00
2
EI
P =
(d) 
0 P =
Q.16 An ac supply gives 
30V
r .m.s. which passes through a 10 W
resistance. The power dissipated in it is
(a) 902 W (b) 90 
W
(c) 452 W (d) 45 
W
DPP/ P 47
3
Q.17 The figure shows variation of R,X
L
 and 
C
X with frequency
f in a series ,, LCR circuit. Then for what frequency
point, the circuit is inductive
f
R
A B C
C
X
L
X
(a)A (b)B (c)C (d) All points
Q.18An alternating e.m.f. of angular frequency wis applied
across an inductance. The instantaneous power developed
in the circuit has an angular frequency
(a)
4
w
(b)
2
w
(c) w (d)
2w
Q.19 In the circuit shown in figure neglecting source resistance
the voltmeter and ammeter reading will respectively , be
A
V
240 V
30 R=W
25
L
X =W
25
C
X =W
(a) 0 ,3 VA (b) 150 ,3 VA
(c) 150 ,6 VA (d) 0 ,8 VA
Q.20 In an LCR circuit, the sharpness of resonance depends on
(a) Inductance (L) (b) Capacitance (C)
(c) Resistance (R) (d) All of these
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 For series LCR circuit, correct statements are
(1) Applied e.m.f. and potential difference across
resistance may be in phase
(2) Applied e.m.f. and potential difference at inductor coil
have phase diffe re nce of p/2
(3) Potential difference across resitance and capacitor
have phase difference of p/2
(4) Potential difference at capacitor and inductor have
phase difference of p/2
Q.22An ac source is connected to a resistive circuits. Which
of the following statements are false?
(1) Current leads the voltage
(2) Current lags behind the voltage
(3) Any of (1) or (2) may be true depending upon the value
of resistance
(4) Current and voltage are in same phase
Q.23 A series LCR arrangement w ith X
L
 = 80 W, X
C
 = 50 W, R = 40 W
is applied across a.c. source of 200 V. Choose the correct
options.
(1) Wattless current = 3.2 A
(2) Power current = 3.2 A
(3) Power factor = 0.6
(4) Impedance of circuit = 50 W
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
A student constructs a series RLC circuit. While operating the
circuit at a frequency f she uses an AC voltmeter and measures
the potential difference across each device as (DV
R
) = 8.8 V,
(DV
L
) = 2.6V and (DV
C
) = 7.4V .
Q.24The circuit is constructed so that the inductor is next to
the capacitor. What result should the student expect for
a measurement of the combined potential difference
(DV
L
 + DV
C
) across the inductor and capacitor ?
(a) 10.0 V (b) 7.8 V
(c) 7.4 V (d) 4.8 V
Q.25 What result should the student expect for a measurement of
the amplitude E
m
 of the potential difference across the power
supply ?
(a) 18.8 V (b) 13.6 V (c) 10.0 V (d) 4.0 V
Page 4


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In a series LCR circuit capacitance is changed from C to 2
C. For the resonant frequency to remain unchanged, the
inductance would be changed from L to
(a) L/2 (b) 2 L (c) 4 L (d) L/4
Q.2 The power factor of 
LCR
circuit at resonance is
(a) 0.707 (b)1 (c) Zero (d) 0.5
Q.3 An alternating current source of frequency 100 Hz is
joined to a combination of a resistance, a capacitance and
a inductance in series. The potential difference across the
inductance, the resistance and the capacitor is 46, 8 and
40 volt respectively . The electromotive force of alternating
current source in volt is
(a) 94 (b) 14 (c) 10 (d) 76
Q.4 A 10 ohm resistance, 5 mH inductance coil and 10 mF
capacitor are joined in series. When a suitable frequency
alternating current source is joined to this combination,
the circuit resonates. If the resistance is halved, the
resonance frequency
(a) is halved (b) is doubled
(c) remains unchanged (d) is quadrupled
Q.5 The phase difference between the current and voltage of
LCR circuit in series combination at resonance is
(a) 0° (b) p/2
(c) p (d)–p
2
DPP/ P 47
Q.6 The coefficient of induction of a choke coil is 0.1H and
resistance is 12W. If it is connected to an alternating current
source of frequency 60 Hz, then power factor is
approximately
(a) 0.4 (b) 0.30 (c) 0.2 (d) 0.1
Q.7 The resonant frequency of a circuit is f. If the capacitance
is made 4 times the initial values, then the resonant
frequency will become
(a) f /2 (b) 2f (c)f (d) f/4
Q.8 In the non-resonant circuit, what will be the nature of the
circuit for frequencies higher than the resonant frequency?
(a) Resistive (b) Capacitive
(c) Inductive (d) None of the above
Q.9 In a series LCR circuit, resistance R = 10W and the impedance
Z = 20W . The phase difference between the current and the
voltage is
(a) 30° (b) 45° (c) 60° (d) 90°
Q.10An alternating e.m.f. of frequency 
1
2
æö
n=
ç÷
èø
p LC
is
applied to a series 
LCR
circuit. For this frequency of the
applied e.m.f.
(a) The circuit is at resonance and its impedance is made
up only of a reactive part
(b) The current in the circuit is not in phase with the
applied e.m.f. and the voltage across R equals this
applied emf
(c) The sum of the p.d.’s across the inductance and
capacitance equals the applied e.m.f. which is 180°
ahead of phase of the current in the circuit
(d) The quality factor of the circuit is 
/ LR w
or 
1/ CR w
and this is a measure of the voltage magnification
(produced by the circuit at resonance) as well as the
sharpness of resonance of the circuit
Q.11 In a circuit L,C and R are connected in series with an
alternating voltage source of frequency f. The current leads
the voltage by 45°. The value of C is
(a)
1
2(2) f fLR p p+
(b)
1
(2) f fLR p p+
(c)
1
2(2) f fLR p p-
(d)
1
(2) f fLR p p-
Q.12 For the series 
LCR
circuit shown in the figure, what is the
resonance frequency and the amplitude of the current at
the resonating frequency
220 V
8 mH
44 W
20µF
(a) 
1
2500rad s
-
 and 5 2A (b) 
1
2500rad s
-
 and 
5A
(c) 
1
2500rad s
-
 and 
5
A
2
(d) 
1
25rad s
-
 and    
5 2A
Q.13 In an ac circuit, V and I are given by 100sin(100 ) Vt = volt,
sin 100 mA
3
It
p æö
=+
ç÷
èø
. The average power dissipated in
circuit is
(a) 10
4
 watt (b) 10 watt
(c) 0.025 watt (d)   2.5 watt
Q.14 For a series LCR circuit R = X
L
 = 2X
C
. The impedance of
the circuit and phase difference between V and I
respectively will be
(a)
1
5R
,tan (2)
2
-
(b)
1
5R
,tan (1/ 2)
2
-
(c)
1
C
5X ,tan (2)
-
(d)
1
5R,tan (1/ 2)
-
Q.15 If a current  I given by 
0
I sin
2
t
p æö
w-
ç÷
èø
 flows in an ac circuit
across which an ac potential of 
0
sin EEt =w has been
applied, then the average power consumption P in the circuit
will be
(a) 
00
2
EI
P =
(b) 
00
2 P El =
(c) 
00
2
EI
P =
(d) 
0 P =
Q.16 An ac supply gives 
30V
r .m.s. which passes through a 10 W
resistance. The power dissipated in it is
(a) 902 W (b) 90 
W
(c) 452 W (d) 45 
W
DPP/ P 47
3
Q.17 The figure shows variation of R,X
L
 and 
C
X with frequency
f in a series ,, LCR circuit. Then for what frequency
point, the circuit is inductive
f
R
A B C
C
X
L
X
(a)A (b)B (c)C (d) All points
Q.18An alternating e.m.f. of angular frequency wis applied
across an inductance. The instantaneous power developed
in the circuit has an angular frequency
(a)
4
w
(b)
2
w
(c) w (d)
2w
Q.19 In the circuit shown in figure neglecting source resistance
the voltmeter and ammeter reading will respectively , be
A
V
240 V
30 R=W
25
L
X =W
25
C
X =W
(a) 0 ,3 VA (b) 150 ,3 VA
(c) 150 ,6 VA (d) 0 ,8 VA
Q.20 In an LCR circuit, the sharpness of resonance depends on
(a) Inductance (L) (b) Capacitance (C)
(c) Resistance (R) (d) All of these
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 For series LCR circuit, correct statements are
(1) Applied e.m.f. and potential difference across
resistance may be in phase
(2) Applied e.m.f. and potential difference at inductor coil
have phase diffe re nce of p/2
(3) Potential difference across resitance and capacitor
have phase difference of p/2
(4) Potential difference at capacitor and inductor have
phase difference of p/2
Q.22An ac source is connected to a resistive circuits. Which
of the following statements are false?
(1) Current leads the voltage
(2) Current lags behind the voltage
(3) Any of (1) or (2) may be true depending upon the value
of resistance
(4) Current and voltage are in same phase
Q.23 A series LCR arrangement w ith X
L
 = 80 W, X
C
 = 50 W, R = 40 W
is applied across a.c. source of 200 V. Choose the correct
options.
(1) Wattless current = 3.2 A
(2) Power current = 3.2 A
(3) Power factor = 0.6
(4) Impedance of circuit = 50 W
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
A student constructs a series RLC circuit. While operating the
circuit at a frequency f she uses an AC voltmeter and measures
the potential difference across each device as (DV
R
) = 8.8 V,
(DV
L
) = 2.6V and (DV
C
) = 7.4V .
Q.24The circuit is constructed so that the inductor is next to
the capacitor. What result should the student expect for
a measurement of the combined potential difference
(DV
L
 + DV
C
) across the inductor and capacitor ?
(a) 10.0 V (b) 7.8 V
(c) 7.4 V (d) 4.8 V
Q.25 What result should the student expect for a measurement of
the amplitude E
m
 of the potential difference across the power
supply ?
(a) 18.8 V (b) 13.6 V (c) 10.0 V (d) 4.0 V
4
DPP/ P 47
Q.26 What will happen to the value of (DV
L
) if the frequency is
adjusted to increase the current through the circuit?
(a)(DV
L
) will increase.
(b)(DV
L
) will decrease.
(c)(DV
L
) will remain the same regardless of any changes
to f.
(d) There is not enough information to answer the
question.
DIRECTIONS (Q. 27-Q.29) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.27Statement-1 : For an electric lamp connected in series
with a variable capacitor and ac source, its brightness
increases  with increase in capacitance.
Statement-2 : Capacitive reactance decreases with
increase in capacitance of capacitor.
Q.28 Statement-1 : When capacitive reactance is smaller than
the inductive reactance in 
LCR
current, e.m.f. leads the
current.
Statement-2 : The phase angle is the angle between the
alternating e.m.f. and alternating current of the circuit.
Q.29Statement-1 : Choke coil is preferred over a resistor to
adjust current in an ac circuit.
Statement-2 : Power factor for inductance is zero.