Alternating Current Practice Questions - DPP for JEE

 Page 1


PART-I (Single Correct MCQs)
1. A coil of inductance 300 mH and resistance 2? is connected to a source
of voltage 2V. The current reaches half of its steady state value in
(a) 0.1 s
(b) 0.05 s
(c) 0.3 s
(d) 0.15 s
2. Consider the RLC circuit shown below connected to an AC source of
constant peak voltage V
0
 and variable  frequency ?
0
. The value of L is
20 mH. For a certain value ?
0 
= ?
1
, rms voltage across L, C, R are
shown in the diagram. At ?
0 
= ?
2
, it is found that rms voltage across
resistance is 50V.  Then
Page 2


PART-I (Single Correct MCQs)
1. A coil of inductance 300 mH and resistance 2? is connected to a source
of voltage 2V. The current reaches half of its steady state value in
(a) 0.1 s
(b) 0.05 s
(c) 0.3 s
(d) 0.15 s
2. Consider the RLC circuit shown below connected to an AC source of
constant peak voltage V
0
 and variable  frequency ?
0
. The value of L is
20 mH. For a certain value ?
0 
= ?
1
, rms voltage across L, C, R are
shown in the diagram. At ?
0 
= ?
2
, it is found that rms voltage across
resistance is 50V.  Then
The value of ?
2
 is
(a)
(b)
(c)
(d)
3. A bulb is rated at 100 V, 100 W, it can be treated as a resistor. Find out
the inductance of an inductor (called choke coil) that should be
connected in series with the bulb to operate the bulb at its rated power
with the help of an ac source of 200 V and 50 Hz.
(a)
(b) 100 H
(c)
(d)
4. An inductor of inductance L = 400 mH and
resistors of resistance R
1
 = 2? and R
2
 = 2? are
connected to a battery of emf 12 V as shown in the
figure. The internal resistance of the battery is
negligible. The switch S is closed at t = 0. The
potential drop across L as a function of time is
`
(a)
(b) 6(1 – e
–t/0.2
)V
(c) 12e
–5t
 V
(d) 6e
–5t
 V
5. An ac source of angular frequency ? is fed across a resistor r and a
Page 3


PART-I (Single Correct MCQs)
1. A coil of inductance 300 mH and resistance 2? is connected to a source
of voltage 2V. The current reaches half of its steady state value in
(a) 0.1 s
(b) 0.05 s
(c) 0.3 s
(d) 0.15 s
2. Consider the RLC circuit shown below connected to an AC source of
constant peak voltage V
0
 and variable  frequency ?
0
. The value of L is
20 mH. For a certain value ?
0 
= ?
1
, rms voltage across L, C, R are
shown in the diagram. At ?
0 
= ?
2
, it is found that rms voltage across
resistance is 50V.  Then
The value of ?
2
 is
(a)
(b)
(c)
(d)
3. A bulb is rated at 100 V, 100 W, it can be treated as a resistor. Find out
the inductance of an inductor (called choke coil) that should be
connected in series with the bulb to operate the bulb at its rated power
with the help of an ac source of 200 V and 50 Hz.
(a)
(b) 100 H
(c)
(d)
4. An inductor of inductance L = 400 mH and
resistors of resistance R
1
 = 2? and R
2
 = 2? are
connected to a battery of emf 12 V as shown in the
figure. The internal resistance of the battery is
negligible. The switch S is closed at t = 0. The
potential drop across L as a function of time is
`
(a)
(b) 6(1 – e
–t/0.2
)V
(c) 12e
–5t
 V
(d) 6e
–5t
 V
5. An ac source of angular frequency ? is fed across a resistor r and a
capacitor C in series. The current registered is I. If now the frequency of
source is changed to ?/3 (but maintaining the same voltage), the current
in the circuit is found to be halved. The ratio of reactance to resistance
at the original frequency ? is
(a)
(b)
(c)
(d)
6. An ideal coil of 10H is connected in series with a resistance of 5? and a
battery of 5V. 2second after the connection is made, the current flowing
in ampere in the circuit is
(a) (1 – e
–1
)
(b) (1 – e)
(c) e
(d) e
–1
7. A fully charged capacitor C with initial charge q
0
 is connected to a coil
of self inductance L at t = 0. The time at  which the energy is stored
equally between the electric and the magnetic fields is:
(a)
(b)
(c)
(d)
8. In an oscillating LC circuit the maximum charge on the capacitor is Q.
The charge on the capacitor when the energy is stored equally between
the electric and magnetic field is
(a)
Page 4


PART-I (Single Correct MCQs)
1. A coil of inductance 300 mH and resistance 2? is connected to a source
of voltage 2V. The current reaches half of its steady state value in
(a) 0.1 s
(b) 0.05 s
(c) 0.3 s
(d) 0.15 s
2. Consider the RLC circuit shown below connected to an AC source of
constant peak voltage V
0
 and variable  frequency ?
0
. The value of L is
20 mH. For a certain value ?
0 
= ?
1
, rms voltage across L, C, R are
shown in the diagram. At ?
0 
= ?
2
, it is found that rms voltage across
resistance is 50V.  Then
The value of ?
2
 is
(a)
(b)
(c)
(d)
3. A bulb is rated at 100 V, 100 W, it can be treated as a resistor. Find out
the inductance of an inductor (called choke coil) that should be
connected in series with the bulb to operate the bulb at its rated power
with the help of an ac source of 200 V and 50 Hz.
(a)
(b) 100 H
(c)
(d)
4. An inductor of inductance L = 400 mH and
resistors of resistance R
1
 = 2? and R
2
 = 2? are
connected to a battery of emf 12 V as shown in the
figure. The internal resistance of the battery is
negligible. The switch S is closed at t = 0. The
potential drop across L as a function of time is
`
(a)
(b) 6(1 – e
–t/0.2
)V
(c) 12e
–5t
 V
(d) 6e
–5t
 V
5. An ac source of angular frequency ? is fed across a resistor r and a
capacitor C in series. The current registered is I. If now the frequency of
source is changed to ?/3 (but maintaining the same voltage), the current
in the circuit is found to be halved. The ratio of reactance to resistance
at the original frequency ? is
(a)
(b)
(c)
(d)
6. An ideal coil of 10H is connected in series with a resistance of 5? and a
battery of 5V. 2second after the connection is made, the current flowing
in ampere in the circuit is
(a) (1 – e
–1
)
(b) (1 – e)
(c) e
(d) e
–1
7. A fully charged capacitor C with initial charge q
0
 is connected to a coil
of self inductance L at t = 0. The time at  which the energy is stored
equally between the electric and the magnetic fields is:
(a)
(b)
(c)
(d)
8. In an oscillating LC circuit the maximum charge on the capacitor is Q.
The charge on the capacitor when the energy is stored equally between
the electric and magnetic field is
(a)
(b)
(c)
(d) Q
9. The tuning circuit of a radio receiver has a resistance of 50?, an
inductor of 10 mH and a variable capacitor. A 1 MHz radio wave
produces a potential difference of 0.1 mV. The values of the capacitor
to produce resonance is (Take p
2
 = 10)
(a) 2.5 pF (b)  5.0 pF (c) 25 pF (d)   50 pF
10. The instantaneous values of alternating current and voltages in a circuit
are given as
amper
 Volt
The average power in Watts consumed in the circuit is :
(a)
(b)
(c)
(d)
11. An inductor (L = 100 mH), a resistor (R = 100 ?) and a battery (E =
100 V) are initially connected in series as shown in the figure. After a
long time the battery is disconnected after short circuiting the points A
and B. The current in the circuit 1 ms after the short circuit is
Page 5


PART-I (Single Correct MCQs)
1. A coil of inductance 300 mH and resistance 2? is connected to a source
of voltage 2V. The current reaches half of its steady state value in
(a) 0.1 s
(b) 0.05 s
(c) 0.3 s
(d) 0.15 s
2. Consider the RLC circuit shown below connected to an AC source of
constant peak voltage V
0
 and variable  frequency ?
0
. The value of L is
20 mH. For a certain value ?
0 
= ?
1
, rms voltage across L, C, R are
shown in the diagram. At ?
0 
= ?
2
, it is found that rms voltage across
resistance is 50V.  Then
The value of ?
2
 is
(a)
(b)
(c)
(d)
3. A bulb is rated at 100 V, 100 W, it can be treated as a resistor. Find out
the inductance of an inductor (called choke coil) that should be
connected in series with the bulb to operate the bulb at its rated power
with the help of an ac source of 200 V and 50 Hz.
(a)
(b) 100 H
(c)
(d)
4. An inductor of inductance L = 400 mH and
resistors of resistance R
1
 = 2? and R
2
 = 2? are
connected to a battery of emf 12 V as shown in the
figure. The internal resistance of the battery is
negligible. The switch S is closed at t = 0. The
potential drop across L as a function of time is
`
(a)
(b) 6(1 – e
–t/0.2
)V
(c) 12e
–5t
 V
(d) 6e
–5t
 V
5. An ac source of angular frequency ? is fed across a resistor r and a
capacitor C in series. The current registered is I. If now the frequency of
source is changed to ?/3 (but maintaining the same voltage), the current
in the circuit is found to be halved. The ratio of reactance to resistance
at the original frequency ? is
(a)
(b)
(c)
(d)
6. An ideal coil of 10H is connected in series with a resistance of 5? and a
battery of 5V. 2second after the connection is made, the current flowing
in ampere in the circuit is
(a) (1 – e
–1
)
(b) (1 – e)
(c) e
(d) e
–1
7. A fully charged capacitor C with initial charge q
0
 is connected to a coil
of self inductance L at t = 0. The time at  which the energy is stored
equally between the electric and the magnetic fields is:
(a)
(b)
(c)
(d)
8. In an oscillating LC circuit the maximum charge on the capacitor is Q.
The charge on the capacitor when the energy is stored equally between
the electric and magnetic field is
(a)
(b)
(c)
(d) Q
9. The tuning circuit of a radio receiver has a resistance of 50?, an
inductor of 10 mH and a variable capacitor. A 1 MHz radio wave
produces a potential difference of 0.1 mV. The values of the capacitor
to produce resonance is (Take p
2
 = 10)
(a) 2.5 pF (b)  5.0 pF (c) 25 pF (d)   50 pF
10. The instantaneous values of alternating current and voltages in a circuit
are given as
amper
 Volt
The average power in Watts consumed in the circuit is :
(a)
(b)
(c)
(d)
11. An inductor (L = 100 mH), a resistor (R = 100 ?) and a battery (E =
100 V) are initially connected in series as shown in the figure. After a
long time the battery is disconnected after short circuiting the points A
and B. The current in the circuit 1 ms after the short circuit is
(a) 1/e A
(b) e A
(c) 0.1 A
(d) 1 A
12. A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz
frequency. If an ac source, of 200 volt, 100 Hz, is connected across the
coil, the current in the coil will be
(a) 4.0 A
(b) 8.0 A
(c)
(d) 2.0 A
13. Which one of the following curves represents the variation of
impedance (Z) with frequency f in series LCR circuit?
(a)
(b)