Alternating Current- 1 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The resistance of a coil for dc is 5 ohm. In ac, the resistance
will
(a) remain same (b) increase
(c) decrease (d) be zero
Q.2 If instantaneous current is given by 4cos() = w +f it
amperes, then the r.m.s. value of current is
(a) 4 ampere (b)
22
ampere
(c)
42
ampere (d) zero ampere
Q.3 In an ac circuit I = 100 sin 200pt. The time required for
the current to achieve its peak value will be
(a)
1
sec
100
(b)
1
sec
200
(c)
1
sec
300
(d)
1
sec
400
Q.4 The frequency of ac mains in India is
(a) 30 c/s or Hz (b) 50 c/s or Hz
(c) 60 c/s or Hz (d) 120 c/s or Hz
Q.5 The peak value of an alternating e.m.f. E given by
0
cos EEt =w is 10 volts and its frequency is 50 Hz. At
time 
1
sec,
600
t = the instantaneous e.m.f. is
(a) 10 V (b) 53 V (c) 5 V (d) 1 V
Page 2


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The resistance of a coil for dc is 5 ohm. In ac, the resistance
will
(a) remain same (b) increase
(c) decrease (d) be zero
Q.2 If instantaneous current is given by 4cos() = w +f it
amperes, then the r.m.s. value of current is
(a) 4 ampere (b)
22
ampere
(c)
42
ampere (d) zero ampere
Q.3 In an ac circuit I = 100 sin 200pt. The time required for
the current to achieve its peak value will be
(a)
1
sec
100
(b)
1
sec
200
(c)
1
sec
300
(d)
1
sec
400
Q.4 The frequency of ac mains in India is
(a) 30 c/s or Hz (b) 50 c/s or Hz
(c) 60 c/s or Hz (d) 120 c/s or Hz
Q.5 The peak value of an alternating e.m.f. E given by
0
cos EEt =w is 10 volts and its frequency is 50 Hz. At
time 
1
sec,
600
t = the instantaneous e.m.f. is
(a) 10 V (b) 53 V (c) 5 V (d) 1 V
2
DPP/ P 46
Q.6 An alternating current is given by the equation
12
cos sin = w+w ii tit . The r.m.s. current is given by
(a) 12
1
()
2
ii +
(b)
2
12
1
()
2
ii +
(c)
2 2 1/2
12
1
()
2
ii +
(d)
2 2 1/2
12
1
()
2
ii +
Q.7 In a circuit, the value of alternating current is measured by
hot wire ammeter as 10 ampere. Its peak value will be
(a) 10 A (b) 20 A (c) 14.14 A (d) 7.07 A
Q.8 The frequency of an alternating voltage is 50 cycles/sec
and its amplitude is 120V. Then the r.m.s. value of voltage
is
(a) 101.3V (b) 84.8V (c) 70.7V (d) 56.5V
Q.9 A resistance of 20W is connected to a source of an
alternating potential 220sin(100 ) Vt =p . The time taken
by the current to change from its peak value to r.m.s. value
is
(a) 0.2 sec (b) 0.25 sec
(c) 25 × 10
–3
 sec (d) 2.5 × 10
–3
 sec
Q.10 An alternating current of frequency f is flowing in a circuit
containing a resistor of resistance 
R
and a choke of
inductance L in series. The impedance of this circuit is
(a) 2 R fL +p (b)
2 2 22
4 R fL +p
(c)
22
RL +
(d)
2
2 R fL +p
Q.11 An alternating voltage is connected in series with a
resistance R and an inductance L. If the potential drop across
the resistance is 200 V and across the inductance is 150 V,
then the applied voltage is
(a) 350 V (b) 250 V
(c) 500 V (d) 300 V
Q.12An inductive circuit contains resistance of 10W and an
inductance of 20 H. If an ac voltage of 120 V and frequency
60 Hz is applied to this circuit, the current would be nearly
(a) 0.32 A (b) 0.016 A
(c) 0.48 A (d) 0.80 A
Q.13 A 20 volt ac is applied to a circuit consisting of a resistance
and a coil with negligible resistance. If the voltage across
the resistance is 12 V , the voltage across the coil is
(a) 16 volt (b) 10 volt
(c) 8 volt (d) 6 volt
Q.14 An alternating voltage 200 2 sin(100 ) Et = is connected
to a 1 microfarad capacitor through an ac ammeter. The
reading of the ammeter will be
(a) 10 mA (b) 20 mA
(c) 40 mA (d) 80 mA
Q.15 A resistor and a capacitor are connected in series with an
a.c. source. If the potential drop across the capacitor is 5
V and that across resistor is 12 V, applied voltage is
(a) 13 V (b) 17 V
(c) 5 V (d) 12 V
Q.16 A 120 volt ac source is connected across a pure inductor
of inductance 0.70 henry . If the frequency of the ac source
is 60 Hz, the current passing through the inductor is
(a) 4.55 amp (b) 0.355 amp
(c) 0.455 amp (d) 3.55 amp
Q.17The instantaneous value of current in an A.C. circuit is
I = 2 sin (100 pt + p/3)A. The current will be maximum
for the first time at
(a) t = 
1
100
s
(b) t = 
1
200
s
(c) t = 
1
400
s
(d) t = 
1
600
s
Q.18 In an L – R circuit, the value of  L is  
0.4 æö
ç÷
p
èø
henry and the
value of R is 30 ohm. If in the circuit, an alternating e.m.f.
of 200 volt at 50 cycles per sec is connected, the
impedance of the circuit and current will be
(a) 11.4 ,17.5A W (b) 30.7 ,6.5A W
(c) 40.4 ,5A W (d) 50 ,4A W
Page 3


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The resistance of a coil for dc is 5 ohm. In ac, the resistance
will
(a) remain same (b) increase
(c) decrease (d) be zero
Q.2 If instantaneous current is given by 4cos() = w +f it
amperes, then the r.m.s. value of current is
(a) 4 ampere (b)
22
ampere
(c)
42
ampere (d) zero ampere
Q.3 In an ac circuit I = 100 sin 200pt. The time required for
the current to achieve its peak value will be
(a)
1
sec
100
(b)
1
sec
200
(c)
1
sec
300
(d)
1
sec
400
Q.4 The frequency of ac mains in India is
(a) 30 c/s or Hz (b) 50 c/s or Hz
(c) 60 c/s or Hz (d) 120 c/s or Hz
Q.5 The peak value of an alternating e.m.f. E given by
0
cos EEt =w is 10 volts and its frequency is 50 Hz. At
time 
1
sec,
600
t = the instantaneous e.m.f. is
(a) 10 V (b) 53 V (c) 5 V (d) 1 V
2
DPP/ P 46
Q.6 An alternating current is given by the equation
12
cos sin = w+w ii tit . The r.m.s. current is given by
(a) 12
1
()
2
ii +
(b)
2
12
1
()
2
ii +
(c)
2 2 1/2
12
1
()
2
ii +
(d)
2 2 1/2
12
1
()
2
ii +
Q.7 In a circuit, the value of alternating current is measured by
hot wire ammeter as 10 ampere. Its peak value will be
(a) 10 A (b) 20 A (c) 14.14 A (d) 7.07 A
Q.8 The frequency of an alternating voltage is 50 cycles/sec
and its amplitude is 120V. Then the r.m.s. value of voltage
is
(a) 101.3V (b) 84.8V (c) 70.7V (d) 56.5V
Q.9 A resistance of 20W is connected to a source of an
alternating potential 220sin(100 ) Vt =p . The time taken
by the current to change from its peak value to r.m.s. value
is
(a) 0.2 sec (b) 0.25 sec
(c) 25 × 10
–3
 sec (d) 2.5 × 10
–3
 sec
Q.10 An alternating current of frequency f is flowing in a circuit
containing a resistor of resistance 
R
and a choke of
inductance L in series. The impedance of this circuit is
(a) 2 R fL +p (b)
2 2 22
4 R fL +p
(c)
22
RL +
(d)
2
2 R fL +p
Q.11 An alternating voltage is connected in series with a
resistance R and an inductance L. If the potential drop across
the resistance is 200 V and across the inductance is 150 V,
then the applied voltage is
(a) 350 V (b) 250 V
(c) 500 V (d) 300 V
Q.12An inductive circuit contains resistance of 10W and an
inductance of 20 H. If an ac voltage of 120 V and frequency
60 Hz is applied to this circuit, the current would be nearly
(a) 0.32 A (b) 0.016 A
(c) 0.48 A (d) 0.80 A
Q.13 A 20 volt ac is applied to a circuit consisting of a resistance
and a coil with negligible resistance. If the voltage across
the resistance is 12 V , the voltage across the coil is
(a) 16 volt (b) 10 volt
(c) 8 volt (d) 6 volt
Q.14 An alternating voltage 200 2 sin(100 ) Et = is connected
to a 1 microfarad capacitor through an ac ammeter. The
reading of the ammeter will be
(a) 10 mA (b) 20 mA
(c) 40 mA (d) 80 mA
Q.15 A resistor and a capacitor are connected in series with an
a.c. source. If the potential drop across the capacitor is 5
V and that across resistor is 12 V, applied voltage is
(a) 13 V (b) 17 V
(c) 5 V (d) 12 V
Q.16 A 120 volt ac source is connected across a pure inductor
of inductance 0.70 henry . If the frequency of the ac source
is 60 Hz, the current passing through the inductor is
(a) 4.55 amp (b) 0.355 amp
(c) 0.455 amp (d) 3.55 amp
Q.17The instantaneous value of current in an A.C. circuit is
I = 2 sin (100 pt + p/3)A. The current will be maximum
for the first time at
(a) t = 
1
100
s
(b) t = 
1
200
s
(c) t = 
1
400
s
(d) t = 
1
600
s
Q.18 In an L – R circuit, the value of  L is  
0.4 æö
ç÷
p
èø
henry and the
value of R is 30 ohm. If in the circuit, an alternating e.m.f.
of 200 volt at 50 cycles per sec is connected, the
impedance of the circuit and current will be
(a) 11.4 ,17.5A W (b) 30.7 ,6.5A W
(c) 40.4 ,5A W (d) 50 ,4A W
DPP/ P 46
3
Q.19The voltage across a pure inductor is represented by the
following diagram. Which one of the following diagrams
will represent the current?
V
t
(a)
t
Ai
(b)
t
Ai
(c)
t
Ai
(d)
t
Ai
Q.20 One 10 V , 60 W bulb is to be connected to 100 V line. The
required induction coil has self-inductance of value
( f = 50 Hz)
(a) 0.052 H (b) 2.42 H
(c) 16.2 mH (d) 1.62 mH
Q.21A resistance of 300W and an inductance of 
1
p
 henry are
connected in series to a ac voltage of 20 volt and 200 Hz
frequency . The phase angle between the voltage and current
is
(a)
1
4
tan
3
-
(b)
1
3
tan
4
-
(c)
1
3
tan
2
-
(d) 
1
2
tan
5
-
DIRECTIONS (Q.22-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.22If an alternating voltage is represented as E = 141 sin
(628t), then
(1) the rms voltage is 141V
(2) the rms voltage is 100V
(3) the frequency is 50 Hz
(4) the frequency is 100 Hz
Q.23 The r.m.s. value of an ac of 50 Hz is 10 A.
(1) The time taken by the alternating current in reaching
from zero to maximum value is 5×10
–3
 sec
(2) The time taken by the alternating current in reaching
from zero to maximum value is 2×10
–3
 sec
(3) The peak current is 14.14 A
(4) The peak current is 7.07 A
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
If the voltage in an ac circuit is represented by the equation,
220 2 V =
sin (314t – f), then
Q.24 RMS value of the voltage is
(a) 220 V (b) 314 V
(c) 220 2V (d) 200/ 2V
Q.25 Average voltage is
(a) 220 V (b) 622/pV
(c) 220 2V (d) 200/ 2V
Q.26Frequency of ac is
(a) 50 Hz (b)
50 2 Hz
(c) 50 2 Hz (d) 75 Hz
Page 4


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The resistance of a coil for dc is 5 ohm. In ac, the resistance
will
(a) remain same (b) increase
(c) decrease (d) be zero
Q.2 If instantaneous current is given by 4cos() = w +f it
amperes, then the r.m.s. value of current is
(a) 4 ampere (b)
22
ampere
(c)
42
ampere (d) zero ampere
Q.3 In an ac circuit I = 100 sin 200pt. The time required for
the current to achieve its peak value will be
(a)
1
sec
100
(b)
1
sec
200
(c)
1
sec
300
(d)
1
sec
400
Q.4 The frequency of ac mains in India is
(a) 30 c/s or Hz (b) 50 c/s or Hz
(c) 60 c/s or Hz (d) 120 c/s or Hz
Q.5 The peak value of an alternating e.m.f. E given by
0
cos EEt =w is 10 volts and its frequency is 50 Hz. At
time 
1
sec,
600
t = the instantaneous e.m.f. is
(a) 10 V (b) 53 V (c) 5 V (d) 1 V
2
DPP/ P 46
Q.6 An alternating current is given by the equation
12
cos sin = w+w ii tit . The r.m.s. current is given by
(a) 12
1
()
2
ii +
(b)
2
12
1
()
2
ii +
(c)
2 2 1/2
12
1
()
2
ii +
(d)
2 2 1/2
12
1
()
2
ii +
Q.7 In a circuit, the value of alternating current is measured by
hot wire ammeter as 10 ampere. Its peak value will be
(a) 10 A (b) 20 A (c) 14.14 A (d) 7.07 A
Q.8 The frequency of an alternating voltage is 50 cycles/sec
and its amplitude is 120V. Then the r.m.s. value of voltage
is
(a) 101.3V (b) 84.8V (c) 70.7V (d) 56.5V
Q.9 A resistance of 20W is connected to a source of an
alternating potential 220sin(100 ) Vt =p . The time taken
by the current to change from its peak value to r.m.s. value
is
(a) 0.2 sec (b) 0.25 sec
(c) 25 × 10
–3
 sec (d) 2.5 × 10
–3
 sec
Q.10 An alternating current of frequency f is flowing in a circuit
containing a resistor of resistance 
R
and a choke of
inductance L in series. The impedance of this circuit is
(a) 2 R fL +p (b)
2 2 22
4 R fL +p
(c)
22
RL +
(d)
2
2 R fL +p
Q.11 An alternating voltage is connected in series with a
resistance R and an inductance L. If the potential drop across
the resistance is 200 V and across the inductance is 150 V,
then the applied voltage is
(a) 350 V (b) 250 V
(c) 500 V (d) 300 V
Q.12An inductive circuit contains resistance of 10W and an
inductance of 20 H. If an ac voltage of 120 V and frequency
60 Hz is applied to this circuit, the current would be nearly
(a) 0.32 A (b) 0.016 A
(c) 0.48 A (d) 0.80 A
Q.13 A 20 volt ac is applied to a circuit consisting of a resistance
and a coil with negligible resistance. If the voltage across
the resistance is 12 V , the voltage across the coil is
(a) 16 volt (b) 10 volt
(c) 8 volt (d) 6 volt
Q.14 An alternating voltage 200 2 sin(100 ) Et = is connected
to a 1 microfarad capacitor through an ac ammeter. The
reading of the ammeter will be
(a) 10 mA (b) 20 mA
(c) 40 mA (d) 80 mA
Q.15 A resistor and a capacitor are connected in series with an
a.c. source. If the potential drop across the capacitor is 5
V and that across resistor is 12 V, applied voltage is
(a) 13 V (b) 17 V
(c) 5 V (d) 12 V
Q.16 A 120 volt ac source is connected across a pure inductor
of inductance 0.70 henry . If the frequency of the ac source
is 60 Hz, the current passing through the inductor is
(a) 4.55 amp (b) 0.355 amp
(c) 0.455 amp (d) 3.55 amp
Q.17The instantaneous value of current in an A.C. circuit is
I = 2 sin (100 pt + p/3)A. The current will be maximum
for the first time at
(a) t = 
1
100
s
(b) t = 
1
200
s
(c) t = 
1
400
s
(d) t = 
1
600
s
Q.18 In an L – R circuit, the value of  L is  
0.4 æö
ç÷
p
èø
henry and the
value of R is 30 ohm. If in the circuit, an alternating e.m.f.
of 200 volt at 50 cycles per sec is connected, the
impedance of the circuit and current will be
(a) 11.4 ,17.5A W (b) 30.7 ,6.5A W
(c) 40.4 ,5A W (d) 50 ,4A W
DPP/ P 46
3
Q.19The voltage across a pure inductor is represented by the
following diagram. Which one of the following diagrams
will represent the current?
V
t
(a)
t
Ai
(b)
t
Ai
(c)
t
Ai
(d)
t
Ai
Q.20 One 10 V , 60 W bulb is to be connected to 100 V line. The
required induction coil has self-inductance of value
( f = 50 Hz)
(a) 0.052 H (b) 2.42 H
(c) 16.2 mH (d) 1.62 mH
Q.21A resistance of 300W and an inductance of 
1
p
 henry are
connected in series to a ac voltage of 20 volt and 200 Hz
frequency . The phase angle between the voltage and current
is
(a)
1
4
tan
3
-
(b)
1
3
tan
4
-
(c)
1
3
tan
2
-
(d) 
1
2
tan
5
-
DIRECTIONS (Q.22-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.22If an alternating voltage is represented as E = 141 sin
(628t), then
(1) the rms voltage is 141V
(2) the rms voltage is 100V
(3) the frequency is 50 Hz
(4) the frequency is 100 Hz
Q.23 The r.m.s. value of an ac of 50 Hz is 10 A.
(1) The time taken by the alternating current in reaching
from zero to maximum value is 5×10
–3
 sec
(2) The time taken by the alternating current in reaching
from zero to maximum value is 2×10
–3
 sec
(3) The peak current is 14.14 A
(4) The peak current is 7.07 A
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
If the voltage in an ac circuit is represented by the equation,
220 2 V =
sin (314t – f), then
Q.24 RMS value of the voltage is
(a) 220 V (b) 314 V
(c) 220 2V (d) 200/ 2V
Q.25 Average voltage is
(a) 220 V (b) 622/pV
(c) 220 2V (d) 200/ 2V
Q.26Frequency of ac is
(a) 50 Hz (b)
50 2 Hz
(c) 50 2 Hz (d) 75 Hz
4
DPP/ P 46
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.
Q27 Statement-1: The alternating current lags behind the em.f.
by a phase angle of p/2, when ac flows through an inductor.
Statement-2 : The inductive reactance increases as the
frequency of ac source decreases.
Q.28 Statement-1 : An alternating current does not show any
magnetic effect.
Statement-2: Alternating current varies with time.
Q.29 Statement-1 : A capacitor of suitable capacitance can be
used in an ac circuit in place of the choke coil.
Statement-2 : A capacitor blocks dc and allows ac only.