DC Pandey Solutions (JEE Main): Alternating Current

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Exercises
For JEE Main
Subjective Questions
Note You can take approximations in the answers.
Q 1.  (a) What is the reactance of a 2.00 H inductor at a frequency of 50.0 Hz?
(b) What is the inductance of an inductor whose reactance is 2.00 ?

at 50.0 Hz?
(c) What is the reactance of a 2.00 ?F

capacitor at a frequency of 50.0 Hz?
(d) What is the capacitance of a capacitor whose reactance is 2.00 ? at 50.0 Hz?
Q 2.  A 300 ? resistor, a 0.250 H inductor, and a 8.00 ?F

capacitor are in series with an ac source with
voltage amplitude 120 V and angular frequency 400 rad/s.
(a) What is the current amplitude?
(b) What is the phase angle of the source voltage with respect to the current? Does the source
voltage lag or lead the current?
(c) What are the voltage amplitudes across the resistor, inductor, and capacitor?
Q 3.  In an L-C-R series circuit, R = 150 ?, L = 0.750 H, and C = 0.0180 ?F.

The source has voltage
amplitude V = 150 V and a frequency equal to the resonance frequency of the circuit.
(a) What is the power factor?
(b) What is the average power delivered by the source?
(c) The capacitor is replaced by one with C = 0.0360 ?B and the source frequency is adjusted to
the new resonance value. Then, what is the average power delivered by the source?
Q 4.  A series circuit has an impedance of 60.0 ? and a power factor of 0.720 at 50.0 Hz. The source
voltage lags the current.
(a) What circuit element, an inductor or a capacitor, should be placed in series with the circuit to
raise its power factor?
(b) What size element will raise the power factor to unity?
Q 5.  Voltage and current for a circuit with two elements in series are expressed as :
V(t) = 170sin(6280t + ?/3) volt
i(t) = 8.5sin(6280t + ?/2)amp
(a) Plot the two waveforms.
(b) Determine the frequency in Hz.
(c) Determine the power factor stating its nature.
(d) What are the values of the elements?
Q 6.  A 5.00 H inductor with negligible resistance is connected across an ac source. Voltage amplitude
is kept constant at 60.0 V but whose frequency can be varied. Find the current amplitude when the
angular, frequency is
(a) 100 rad/s (b) 1000 rad/s (c) 10000 rad/s
Q 7.  A 300 ?

resistor is connected in series with a 0.800 H inductor. The voltage across the resistor as a
function of time is V
R
= (2.50 V)cos [(950rad/s)t].
(a) Derive an expression for the circuit current.
(b) Determine the inductive reactance of the inductor.
(c) Derive an expression for the voltage V
L
across the inductor.
Q 8.  An L-C-R series circuit with L = 0.120 H, R = 240 ?, and C = 7.30 ?F

carries an rms current of
0.450 A with a frequency of 400 Hz.
(a) What are the phase angle and power factor for this circuit?
Page 2

Exercises
For JEE Main
Subjective Questions
Note You can take approximations in the answers.
Q 1.  (a) What is the reactance of a 2.00 H inductor at a frequency of 50.0 Hz?
(b) What is the inductance of an inductor whose reactance is 2.00 ?

at 50.0 Hz?
(c) What is the reactance of a 2.00 ?F

capacitor at a frequency of 50.0 Hz?
(d) What is the capacitance of a capacitor whose reactance is 2.00 ? at 50.0 Hz?
Q 2.  A 300 ? resistor, a 0.250 H inductor, and a 8.00 ?F

capacitor are in series with an ac source with
voltage amplitude 120 V and angular frequency 400 rad/s.
(a) What is the current amplitude?
(b) What is the phase angle of the source voltage with respect to the current? Does the source
voltage lag or lead the current?
(c) What are the voltage amplitudes across the resistor, inductor, and capacitor?
Q 3.  In an L-C-R series circuit, R = 150 ?, L = 0.750 H, and C = 0.0180 ?F.

The source has voltage
amplitude V = 150 V and a frequency equal to the resonance frequency of the circuit.
(a) What is the power factor?
(b) What is the average power delivered by the source?
(c) The capacitor is replaced by one with C = 0.0360 ?B and the source frequency is adjusted to
the new resonance value. Then, what is the average power delivered by the source?
Q 4.  A series circuit has an impedance of 60.0 ? and a power factor of 0.720 at 50.0 Hz. The source
voltage lags the current.
(a) What circuit element, an inductor or a capacitor, should be placed in series with the circuit to
raise its power factor?
(b) What size element will raise the power factor to unity?
Q 5.  Voltage and current for a circuit with two elements in series are expressed as :
V(t) = 170sin(6280t + ?/3) volt
i(t) = 8.5sin(6280t + ?/2)amp
(a) Plot the two waveforms.
(b) Determine the frequency in Hz.
(c) Determine the power factor stating its nature.
(d) What are the values of the elements?
Q 6.  A 5.00 H inductor with negligible resistance is connected across an ac source. Voltage amplitude
is kept constant at 60.0 V but whose frequency can be varied. Find the current amplitude when the
angular, frequency is
(a) 100 rad/s (b) 1000 rad/s (c) 10000 rad/s
Q 7.  A 300 ?

resistor is connected in series with a 0.800 H inductor. The voltage across the resistor as a
function of time is V
R
= (2.50 V)cos [(950rad/s)t].
(a) Derive an expression for the circuit current.
(b) Determine the inductive reactance of the inductor.
(c) Derive an expression for the voltage V
L
across the inductor.
Q 8.  An L-C-R series circuit with L = 0.120 H, R = 240 ?, and C = 7.30 ?F

carries an rms current of
0.450 A with a frequency of 400 Hz.
(a) What are the phase angle and power factor for this circuit?
(b) What is the impedance of the circuit?
(c) What is the rms voltage of the source?
(d) What average power is delivered by the source?
(e) What is the average rate at which electrical energy is converted to thermal energy in the
resistor?
(f) What is the average rate at which electrical energy is dissipated ( converted to other forms) in
the capacitor?
(g) In the inductor?
Solutions
1.  (a)X
L
=2?fL
(b)
(c)
(d)
2.  X
L
= ?L = 100 ?

(a)
(b) Since X
C
> X
L
, voltage lags the current by an angle given by

(c) (V
0
)
R
= I
0
R = (0.326) 300 = 97.8 V
(V
0
)
L
= I
0
X
L
= (0.326) (100) = 32.6 V
(V
0
)
C
= I
0
X
C
= (0.326) (312.5) = 102 V
3.  (a) At resonance frequency, X
L
= X
C
, Z = R and power factor

(b)
(c) Again P = = 75 W
4.  (a) Voltage lags
X
C
> X
L

Power factor,

To increase the power factor denominator should decrease.
Hence X
L
should increase. Therefore an inductor is required to be connected.
(b)
R = 0.72 Z = 0.72 × 60 = 43.2 ?
{X
C
- X
L
)
Page 3

Exercises
For JEE Main
Subjective Questions
Note You can take approximations in the answers.
Q 1.  (a) What is the reactance of a 2.00 H inductor at a frequency of 50.0 Hz?
(b) What is the inductance of an inductor whose reactance is 2.00 ?

at 50.0 Hz?
(c) What is the reactance of a 2.00 ?F

capacitor at a frequency of 50.0 Hz?
(d) What is the capacitance of a capacitor whose reactance is 2.00 ? at 50.0 Hz?
Q 2.  A 300 ? resistor, a 0.250 H inductor, and a 8.00 ?F

capacitor are in series with an ac source with
voltage amplitude 120 V and angular frequency 400 rad/s.
(a) What is the current amplitude?
(b) What is the phase angle of the source voltage with respect to the current? Does the source
voltage lag or lead the current?
(c) What are the voltage amplitudes across the resistor, inductor, and capacitor?
Q 3.  In an L-C-R series circuit, R = 150 ?, L = 0.750 H, and C = 0.0180 ?F.

The source has voltage
amplitude V = 150 V and a frequency equal to the resonance frequency of the circuit.
(a) What is the power factor?
(b) What is the average power delivered by the source?
(c) The capacitor is replaced by one with C = 0.0360 ?B and the source frequency is adjusted to
the new resonance value. Then, what is the average power delivered by the source?
Q 4.  A series circuit has an impedance of 60.0 ? and a power factor of 0.720 at 50.0 Hz. The source
voltage lags the current.
(a) What circuit element, an inductor or a capacitor, should be placed in series with the circuit to
raise its power factor?
(b) What size element will raise the power factor to unity?
Q 5.  Voltage and current for a circuit with two elements in series are expressed as :
V(t) = 170sin(6280t + ?/3) volt
i(t) = 8.5sin(6280t + ?/2)amp
(a) Plot the two waveforms.
(b) Determine the frequency in Hz.
(c) Determine the power factor stating its nature.
(d) What are the values of the elements?
Q 6.  A 5.00 H inductor with negligible resistance is connected across an ac source. Voltage amplitude
is kept constant at 60.0 V but whose frequency can be varied. Find the current amplitude when the
angular, frequency is
(a) 100 rad/s (b) 1000 rad/s (c) 10000 rad/s
Q 7.  A 300 ?

resistor is connected in series with a 0.800 H inductor. The voltage across the resistor as a
function of time is V
R
= (2.50 V)cos [(950rad/s)t].
(a) Derive an expression for the circuit current.
(b) Determine the inductive reactance of the inductor.
(c) Derive an expression for the voltage V
L
across the inductor.
Q 8.  An L-C-R series circuit with L = 0.120 H, R = 240 ?, and C = 7.30 ?F

carries an rms current of
0.450 A with a frequency of 400 Hz.
(a) What are the phase angle and power factor for this circuit?
(b) What is the impedance of the circuit?
(c) What is the rms voltage of the source?
(d) What average power is delivered by the source?
(e) What is the average rate at which electrical energy is converted to thermal energy in the
resistor?
(f) What is the average rate at which electrical energy is dissipated ( converted to other forms) in
the capacitor?
(g) In the inductor?
Solutions
1.  (a)X
L
=2?fL
(b)
(c)
(d)
2.  X
L
= ?L = 100 ?

(a)
(b) Since X
C
> X
L
, voltage lags the current by an angle given by

(c) (V
0
)
R
= I
0
R = (0.326) 300 = 97.8 V
(V
0
)
L
= I
0
X
L
= (0.326) (100) = 32.6 V
(V
0
)
C
= I
0
X
C
= (0.326) (312.5) = 102 V
3.  (a) At resonance frequency, X
L
= X
C
, Z = R and power factor

(b)
(c) Again P = = 75 W
4.  (a) Voltage lags
X
C
> X
L

Power factor,

To increase the power factor denominator should decrease.
Hence X
L
should increase. Therefore an inductor is required to be connected.
(b)
R = 0.72 Z = 0.72 × 60 = 43.2 ?
{X
C
- X
L
)
New inductor of inductance 41.64 ? should be added in the circuit.

5.  (b)
(c)
Power factor = cos ? = cos 30°

From the given functions of V and i we can see that current function leads the voltage function.
(d)

= 10 ?

= 15.92 × 10
-6
F
6.
7.  (a) A
= 8.33 mA
Current function and V
R
function are in phase. Hence,
I = (8.33 mA) cos [(950 rad/s) t]
(b) X
L
= ?L

= 950 × 0.8 = 760 ?
(c) (V
0
)
L
= I
0
X
L
= (8.33 × 10
-3
) (760)
= 6.33V
Now, V
L
function leads the current (or V
R
) function by 90°.
F
L
= 6.33 cos(950t + 90°) = - 6.33 sin (950 t)
8.  X
L
=2 ? fL = 301?
X
C
= = 55?

= 343?
(a)

= 45.6°
Page 4

Exercises
For JEE Main
Subjective Questions
Note You can take approximations in the answers.
Q 1.  (a) What is the reactance of a 2.00 H inductor at a frequency of 50.0 Hz?
(b) What is the inductance of an inductor whose reactance is 2.00 ?

at 50.0 Hz?
(c) What is the reactance of a 2.00 ?F

capacitor at a frequency of 50.0 Hz?
(d) What is the capacitance of a capacitor whose reactance is 2.00 ? at 50.0 Hz?
Q 2.  A 300 ? resistor, a 0.250 H inductor, and a 8.00 ?F

capacitor are in series with an ac source with
voltage amplitude 120 V and angular frequency 400 rad/s.
(a) What is the current amplitude?
(b) What is the phase angle of the source voltage with respect to the current? Does the source
voltage lag or lead the current?
(c) What are the voltage amplitudes across the resistor, inductor, and capacitor?
Q 3.  In an L-C-R series circuit, R = 150 ?, L = 0.750 H, and C = 0.0180 ?F.

The source has voltage
amplitude V = 150 V and a frequency equal to the resonance frequency of the circuit.
(a) What is the power factor?
(b) What is the average power delivered by the source?
(c) The capacitor is replaced by one with C = 0.0360 ?B and the source frequency is adjusted to
the new resonance value. Then, what is the average power delivered by the source?
Q 4.  A series circuit has an impedance of 60.0 ? and a power factor of 0.720 at 50.0 Hz. The source
voltage lags the current.
(a) What circuit element, an inductor or a capacitor, should be placed in series with the circuit to
raise its power factor?
(b) What size element will raise the power factor to unity?
Q 5.  Voltage and current for a circuit with two elements in series are expressed as :
V(t) = 170sin(6280t + ?/3) volt
i(t) = 8.5sin(6280t + ?/2)amp
(a) Plot the two waveforms.
(b) Determine the frequency in Hz.
(c) Determine the power factor stating its nature.
(d) What are the values of the elements?
Q 6.  A 5.00 H inductor with negligible resistance is connected across an ac source. Voltage amplitude
is kept constant at 60.0 V but whose frequency can be varied. Find the current amplitude when the
angular, frequency is
(a) 100 rad/s (b) 1000 rad/s (c) 10000 rad/s
Q 7.  A 300 ?

resistor is connected in series with a 0.800 H inductor. The voltage across the resistor as a
function of time is V
R
= (2.50 V)cos [(950rad/s)t].
(a) Derive an expression for the circuit current.
(b) Determine the inductive reactance of the inductor.
(c) Derive an expression for the voltage V
L
across the inductor.
Q 8.  An L-C-R series circuit with L = 0.120 H, R = 240 ?, and C = 7.30 ?F

carries an rms current of
0.450 A with a frequency of 400 Hz.
(a) What are the phase angle and power factor for this circuit?
(b) What is the impedance of the circuit?
(c) What is the rms voltage of the source?
(d) What average power is delivered by the source?
(e) What is the average rate at which electrical energy is converted to thermal energy in the
resistor?
(f) What is the average rate at which electrical energy is dissipated ( converted to other forms) in
the capacitor?
(g) In the inductor?
Solutions
1.  (a)X
L
=2?fL
(b)
(c)
(d)
2.  X
L
= ?L = 100 ?

(a)
(b) Since X
C
> X
L
, voltage lags the current by an angle given by

(c) (V
0
)
R
= I
0
R = (0.326) 300 = 97.8 V
(V
0
)
L
= I
0
X
L
= (0.326) (100) = 32.6 V
(V
0
)
C
= I
0
X
C
= (0.326) (312.5) = 102 V
3.  (a) At resonance frequency, X
L
= X
C
, Z = R and power factor

(b)
(c) Again P = = 75 W
4.  (a) Voltage lags
X
C
> X
L

Power factor,

To increase the power factor denominator should decrease.
Hence X
L
should increase. Therefore an inductor is required to be connected.
(b)
R = 0.72 Z = 0.72 × 60 = 43.2 ?
{X
C
- X
L
)
New inductor of inductance 41.64 ? should be added in the circuit.

5.  (b)
(c)
Power factor = cos ? = cos 30°

From the given functions of V and i we can see that current function leads the voltage function.
(d)

= 10 ?

= 15.92 × 10
-6
F
6.
7.  (a) A
= 8.33 mA
Current function and V
R
function are in phase. Hence,
I = (8.33 mA) cos [(950 rad/s) t]
(b) X
L
= ?L

= 950 × 0.8 = 760 ?
(c) (V
0
)
L
= I
0
X
L
= (8.33 × 10
-3
) (760)
= 6.33V
Now, V
L
function leads the current (or V
R
) function by 90°.
F
L
= 6.33 cos(950t + 90°) = - 6.33 sin (950 t)
8.  X
L
=2 ? fL = 301?
X
C
= = 55?

= 343?
(a)

= 45.6°

= 0.699
Since X
L
> X
C
, voltage leads the current.
(b) Impedance = Z = 343 ?
(c) V
rms
= I
rms
Z
= 0.45 × 343 = 155 V
(d)
2
rms
P I R ?
= (0.45)
2
(240) = 48.6W
(e) P = P
R
= 48.6 W
(f) P
C
= 0
(g) P
L
= 0

Objective Questions
Single Correct Option
Q 1.  The term cos ?

in an AC circuit is called
(a) form factor  (b) phase factor (c) power factor  (d) quality factor
Q 2.  A DC ammeter cannot measure alternating current because
(a) AC changes its direction   (b) DC instruments will measure the average value
(c) AC can damage the DC instrument (d) AC produces more heat
Q 3.  As the frequency of an alternating current increases the impedance of the circuit
(a) increases continuously    (b) decreases continuously
(c) remains constant     (d) None of these
Q 4.  Phaser diagram of a series AC circuit is shown in figure. Then

(a) The circuit must be containing resistor and capacitor only
(b) The circuit must be containing resistor and inductor only
(c) The circuit must be containing all three elements L, C and R
(d) The circuit cannot have only capacitor and inductor
Q 5.  The rms value of an alternating current
(a) is equal to 0.707 times peak value  (b) is equal to 0.636 times peak value
(c) is equal to 2 times the peak value  (d) None of the above
Q 6.  In an AC circuit the applied potential difference and the current flowing are given by :
V = 200 sin 1 00t volt, I = 5 sin 100t
2
? ??
?
??
??
amp
The power consumption is equal to
(a) 1000 W   (b) 40 W   (c) 20 W   (d) zero
Q 7.  The impedance of a series L-C-R circuit in an AC circuit is
(a)
LC
R (X X ) ?? (b)
22
LC
R (X X ) ??  (c) R    (d) None of these
Page 5

Exercises
For JEE Main
Subjective Questions
Note You can take approximations in the answers.
Q 1.  (a) What is the reactance of a 2.00 H inductor at a frequency of 50.0 Hz?
(b) What is the inductance of an inductor whose reactance is 2.00 ?

at 50.0 Hz?
(c) What is the reactance of a 2.00 ?F

capacitor at a frequency of 50.0 Hz?
(d) What is the capacitance of a capacitor whose reactance is 2.00 ? at 50.0 Hz?
Q 2.  A 300 ? resistor, a 0.250 H inductor, and a 8.00 ?F

capacitor are in series with an ac source with
voltage amplitude 120 V and angular frequency 400 rad/s.
(a) What is the current amplitude?
(b) What is the phase angle of the source voltage with respect to the current? Does the source
voltage lag or lead the current?
(c) What are the voltage amplitudes across the resistor, inductor, and capacitor?
Q 3.  In an L-C-R series circuit, R = 150 ?, L = 0.750 H, and C = 0.0180 ?F.

The source has voltage
amplitude V = 150 V and a frequency equal to the resonance frequency of the circuit.
(a) What is the power factor?
(b) What is the average power delivered by the source?
(c) The capacitor is replaced by one with C = 0.0360 ?B and the source frequency is adjusted to
the new resonance value. Then, what is the average power delivered by the source?
Q 4.  A series circuit has an impedance of 60.0 ? and a power factor of 0.720 at 50.0 Hz. The source
voltage lags the current.
(a) What circuit element, an inductor or a capacitor, should be placed in series with the circuit to
raise its power factor?
(b) What size element will raise the power factor to unity?
Q 5.  Voltage and current for a circuit with two elements in series are expressed as :
V(t) = 170sin(6280t + ?/3) volt
i(t) = 8.5sin(6280t + ?/2)amp
(a) Plot the two waveforms.
(b) Determine the frequency in Hz.
(c) Determine the power factor stating its nature.
(d) What are the values of the elements?
Q 6.  A 5.00 H inductor with negligible resistance is connected across an ac source. Voltage amplitude
is kept constant at 60.0 V but whose frequency can be varied. Find the current amplitude when the
angular, frequency is
(a) 100 rad/s (b) 1000 rad/s (c) 10000 rad/s
Q 7.  A 300 ?

resistor is connected in series with a 0.800 H inductor. The voltage across the resistor as a
function of time is V
R
= (2.50 V)cos [(950rad/s)t].
(a) Derive an expression for the circuit current.
(b) Determine the inductive reactance of the inductor.
(c) Derive an expression for the voltage V
L
across the inductor.
Q 8.  An L-C-R series circuit with L = 0.120 H, R = 240 ?, and C = 7.30 ?F

carries an rms current of
0.450 A with a frequency of 400 Hz.
(a) What are the phase angle and power factor for this circuit?
(b) What is the impedance of the circuit?
(c) What is the rms voltage of the source?
(d) What average power is delivered by the source?
(e) What is the average rate at which electrical energy is converted to thermal energy in the
resistor?
(f) What is the average rate at which electrical energy is dissipated ( converted to other forms) in
the capacitor?
(g) In the inductor?
Solutions
1.  (a)X
L
=2?fL
(b)
(c)
(d)
2.  X
L
= ?L = 100 ?

(a)
(b) Since X
C
> X
L
, voltage lags the current by an angle given by

(c) (V
0
)
R
= I
0
R = (0.326) 300 = 97.8 V
(V
0
)
L
= I
0
X
L
= (0.326) (100) = 32.6 V
(V
0
)
C
= I
0
X
C
= (0.326) (312.5) = 102 V
3.  (a) At resonance frequency, X
L
= X
C
, Z = R and power factor

(b)
(c) Again P = = 75 W
4.  (a) Voltage lags
X
C
> X
L

Power factor,

To increase the power factor denominator should decrease.
Hence X
L
should increase. Therefore an inductor is required to be connected.
(b)
R = 0.72 Z = 0.72 × 60 = 43.2 ?
{X
C
- X
L
)
New inductor of inductance 41.64 ? should be added in the circuit.

5.  (b)
(c)
Power factor = cos ? = cos 30°

From the given functions of V and i we can see that current function leads the voltage function.
(d)

= 10 ?

= 15.92 × 10
-6
F
6.
7.  (a) A
= 8.33 mA
Current function and V
R
function are in phase. Hence,
I = (8.33 mA) cos [(950 rad/s) t]
(b) X
L
= ?L

= 950 × 0.8 = 760 ?
(c) (V
0
)
L
= I
0
X
L
= (8.33 × 10
-3
) (760)
= 6.33V
Now, V
L
function leads the current (or V
R
) function by 90°.
F
L
= 6.33 cos(950t + 90°) = - 6.33 sin (950 t)
8.  X
L
=2 ? fL = 301?
X
C
= = 55?

= 343?
(a)

= 45.6°

= 0.699
Since X
L
> X
C
, voltage leads the current.
(b) Impedance = Z = 343 ?
(c) V
rms
= I
rms
Z
= 0.45 × 343 = 155 V
(d)
2
rms
P I R ?
= (0.45)
2
(240) = 48.6W
(e) P = P
R
= 48.6 W
(f) P
C
= 0
(g) P
L
= 0

Objective Questions
Single Correct Option
Q 1.  The term cos ?

in an AC circuit is called
(a) form factor  (b) phase factor (c) power factor  (d) quality factor
Q 2.  A DC ammeter cannot measure alternating current because
(a) AC changes its direction   (b) DC instruments will measure the average value
(c) AC can damage the DC instrument (d) AC produces more heat
Q 3.  As the frequency of an alternating current increases the impedance of the circuit
(a) increases continuously    (b) decreases continuously
(c) remains constant     (d) None of these
Q 4.  Phaser diagram of a series AC circuit is shown in figure. Then

(a) The circuit must be containing resistor and capacitor only
(b) The circuit must be containing resistor and inductor only
(c) The circuit must be containing all three elements L, C and R
(d) The circuit cannot have only capacitor and inductor
Q 5.  The rms value of an alternating current
(a) is equal to 0.707 times peak value  (b) is equal to 0.636 times peak value
(c) is equal to 2 times the peak value  (d) None of the above
Q 6.  In an AC circuit the applied potential difference and the current flowing are given by :
V = 200 sin 1 00t volt, I = 5 sin 100t
2
? ??
?
??
??
amp
The power consumption is equal to
(a) 1000 W   (b) 40 W   (c) 20 W   (d) zero
Q 7.  The impedance of a series L-C-R circuit in an AC circuit is
(a)
LC
R (X X ) ?? (b)
22
LC
R (X X ) ??  (c) R    (d) None of these
Q 8.  If V
0
and I
0
are the peak current and voltage across the resistor in a series L-C-R circuit, then the
power dissipated in the circuit is
(a)
00
VI
2
(b)
00
VI
2
(c) V
0
I
0
cos ?   (d)
00
VI
cos
2
?
Q 9.  A generator produces a time varying voltage given by V = 240 sin 1201, where t is in second. The
rms voltage and frequency are
(a) 170 V and 19 Hz  (b) 240 V and 60 Hz  (c) 170 V and 60 Hz  (d) 120 V and 19 Hz
Q 10.  An L-C-R series circuit has a maximum current of 5 A. If L= 0.5H and C = 8 ?F, then the angular
frequency of AC voltage is
(a) 500rad/s   (b) 5000rad/s  (c) 400 rad/s   (d) 250 rad/s
Q 11.  The current and voltage functions in an AC circuit are
i = 100 sin 100/mA, V =100sin 100t V
3
? ??
?
??
??

The power dissipated in the circuit is
(a) 10W   (b) 2.5 W   (c) 5 W   (d) 5 kW
Q 12.  A capacitor becomes a perfect insulator for
(a) alternating current (b) direct current  (c) both (a) and (b)  (d) None of these
Q 13.  For an alternating voltage V = 10 cos 100 ?t volt, the instantaneous voltage at
1
t
600
? s is
(a) 1 V   (b) 5 V   (c) 5 3V   (d) 10 V
Q 14.  In a purely resistive AC circuit
(a) voltage leads current    (b) voltage lags current
(c) voltage and current are in same phase  (d) nothing can be said
Q 15.  Identify the graph which correctly represents the variation of capacitive reactance X
C
with
frequency
(a)   (b)  (c)  (d)
Q 16.  In an AC circuit, the impedance is 3 times the reactance, then the phase angle is
(a) 60°   (b) 30°   (c) zero   (d) None of these
Q 17.  Voltage applied to an AC circuit and current flowing in it is given by
V 200 2 sin t and i 2 cos t
44
?? ? ? ? ?
? ? ? ? ? ? ?
? ? ? ?
? ? ? ?

Then power consumed in the circuit will be
(a) 200 W   (b) 400 W   (c) 200 2W   (d) None of these
Q 18.  When 100 volt DC source is applied across a coil, a current of 1 A flows through it. When 100 V
AC source of 50 Hz is applied to the same coil, only 0.5 A current flows. Calculate the inductance
of the coil
(a) ( ?/ 3 )H  (b) ( 3 / ?)H  (c) (2/ ?)H   (d) None of these
Q 19.  In the circuit shown in figure, the reading of the AC ammeter is
```

209 docs

## FAQs on DC Pandey Solutions (JEE Main): Alternating Current - DC Pandey Solutions for JEE Physics

 1. What is alternating current (AC)?
Ans. Alternating current (AC) is an electric current that periodically reverses direction. In AC, the flow of electric charge changes direction at regular intervals, usually 50 or 60 times per second. This is in contrast to direct current (DC), where the flow of charge is always in one direction.
 2. How is alternating current generated?
Ans. Alternating current can be generated using devices called alternators or generators. These devices use the principle of electromagnetic induction to produce an alternating current. When a coil of wire is rotated in a magnetic field, an alternating current is induced in the wire.
 3. What are the advantages of alternating current over direct current?
Ans. Alternating current has several advantages over direct current. One of the main advantages is that AC can be easily transmitted over long distances without significant loss of energy. AC can also be easily stepped up or down in voltage using transformers. Additionally, AC allows for the use of more efficient and cost-effective power generation and distribution systems.
 4. What is the frequency of alternating current in most household circuits?
Ans. The frequency of alternating current in most household circuits is 50 or 60 Hz. In countries like India, the frequency is typically 50 Hz, while in countries like the United States, the frequency is typically 60 Hz. This means that the direction of current changes 50 or 60 times per second.
 5. How is alternating current measured?
Ans. Alternating current is measured using a device called an ammeter. An ammeter is connected in series with the circuit and measures the current flowing through it. The reading on the ammeter gives the value of the alternating current in amperes (A). It is important to note that the ammeter should be able to measure the frequency of the alternating current accurately.

## DC Pandey Solutions for JEE Physics

209 docs

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