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All questions of Alternating Current for NEET Exam
In a region of uniform magnetic inductionB = 10–2 tesla, a circular coil of radius 30 cm andresistance π2 ohm is rotated about an axis whichis perpendicular to the direction of B and whichforms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating currentinduced in the coil is [1988]- a)4π2 mA
- b)30 mA
- c)6 mA
- d)200 mA
Correct answer is option 'C'. Can you explain this answer?
In a region of uniform magnetic inductionB = 10–2 tesla, a circular coil of radius 30 cm andresistance π2 ohm is rotated about an axis whichis perpendicular to the direction of B and whichforms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating currentinduced in the coil is [1988]
a)
4π2 mA
b)
30 mA
c)
6 mA
d)
200 mA
|
Shalini Saha answered |
Given, n = 1, B = 10–2 T,
A = π(0.3)2m2, R = π2
f= (200/60) and ω = 2π(200/60)
Substituting these values and solving, we
get
I0 = 6 × 10–3 A = 6mA
A = π(0.3)2m2, R = π2
f= (200/60) and ω = 2π(200/60)
Substituting these values and solving, we
get
I0 = 6 × 10–3 A = 6mA
In an ac circuit an alternating voltage e = 200 √2 sin 100 t volts is connected to a capacitorof capacity 1μF. The r.m.s. value of the currentin the circuit is [2011]- a)10 mA
- b)100 mA
- c)200 mA
- d)20 mA
Correct answer is option 'D'. Can you explain this answer?
In an ac circuit an alternating voltage e = 200 √2 sin 100 t volts is connected to a capacitorof capacity 1μF. The r.m.s. value of the currentin the circuit is [2011]
a)
10 mA
b)
100 mA
c)
200 mA
d)
20 mA
|
Lalit Yadav answered |
given e=200√2sin100t
ω=100 rad/sec
Erms= 200√2/√2
C=1×10−6
Z=Xc=1/ωC=1/100×10−6=104Ω
I=Erms/Z=(200√2/√2)/104 =2×10−2A=20mA
ω=100 rad/sec
Erms= 200√2/√2
C=1×10−6
Z=Xc=1/ωC=1/100×10−6=104Ω
I=Erms/Z=(200√2/√2)/104 =2×10−2A=20mA
The r.m.s. value of potential difference V shown in the figure is [2011M]
- a)V0
- b)V0/√2
- c)V0/2
- d)V0/√3
Correct answer is option 'B'. Can you explain this answer?
The r.m.s. value of potential difference V shown in the figure is [2011M]
a)
V0
b)
V0/√2
c)
V0/2
d)
V0/√3
|
Rohit Jain answered |
Voltage is given as V=Vo for 0 ≥ t ≤ T/2
=0 for T/2 ≥ t ≤T
Rms voltage
⟹ Vrms=Vo/√2
=0 for T/2 ≥ t ≤T
Rms voltage
⟹ Vrms=Vo/√2
In which of the following, emission of electronsdoes not take place [1990]- a)thermionic emission
- b)X-rays emission
- c)photoelectric emission
- d)secondary emission
Correct answer is option 'B'. Can you explain this answer?
In which of the following, emission of electronsdoes not take place [1990]
a)
thermionic emission
b)
X-rays emission
c)
photoelectric emission
d)
secondary emission
|
Lekshmi Banerjee answered |
Thermionic emission : When a metal is
heated to a high temperature, the free
electrons gain kinetic energy and escape
from the surface of the metal.
Secondary emission : When an electron
strikes the surface of a metallic plate, it emits
other electrons from the surface.
Photoelectric emission : Emission of
electrons from the metal surface on irradiation
with radiation of suitable frequency.
X-rays emission : High speed electrons
(emitted from a filament) striking a target
(a copper block) to emit X-rays.
heated to a high temperature, the free
electrons gain kinetic energy and escape
from the surface of the metal.
Secondary emission : When an electron
strikes the surface of a metallic plate, it emits
other electrons from the surface.
Photoelectric emission : Emission of
electrons from the metal surface on irradiation
with radiation of suitable frequency.
X-rays emission : High speed electrons
(emitted from a filament) striking a target
(a copper block) to emit X-rays.
The current (I) in the inductance is varying with time according to the plot shown in figure. [2012]
Which one of the following is the correct variation of voltage with time in the coil?- a)
- b)
- c)
- d)
Correct answer is option 'D'. Can you explain this answer?
The current (I) in the inductance is varying with time according to the plot shown in figure. [2012]
Which one of the following is the correct variation of voltage with time in the coil?
a)
b)
c)
d)
|
Dipika Das answered |
Here
time and di/dt is -ve for next T/2 time so.
time and di/dt is -ve for next T/2 time so.The time constant of C–R circuit is [1992]- a)1/CR
- b)C/R
- c)CR
- d)R/C
Correct answer is option 'C'. Can you explain this answer?
The time constant of C–R circuit is [1992]
a)
1/CR
b)
C/R
c)
CR
d)
R/C
|
Arpita Tiwari answered |
The time constant for resonance circuit,
C = CR
Growth of charge in a circuit containing
capacitance and resistance is given by the
formula,
C = CR
Growth of charge in a circuit containing
capacitance and resistance is given by the
formula,
CR is known as time constant in this formula.
A coil of inductive reactance 31 Ω has aresistance of 8 Ω. It is placed in series with acondenser of capacitative reactance 25Ω. Thecombination is connected to an a.c. source of110 volt. The power factor of the circuit is[2006]- a)0.64
- b)0.80
- c)0.33
- d)0.56
Correct answer is option 'B'. Can you explain this answer?
A coil of inductive reactance 31 Ω has aresistance of 8 Ω. It is placed in series with acondenser of capacitative reactance 25Ω. Thecombination is connected to an a.c. source of110 volt. The power factor of the circuit is[2006]
a)
0.64
b)
0.80
c)
0.33
d)
0.56
|
Nayanika Dasgupta answered |
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 [2011M]- a)4.0 A
- b)8.0 A
- c)
- d)2.0 A
Correct answer is option 'A'. Can you explain this answer?
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 [2011M]
a)
4.0 A
b)
8.0 A
c)
d)
2.0 A
|
Diya Datta answered |
If ω = 50 × 2π then ωL = 20Ω
If ω' = 100 × 2π then ω'L = 40Ω
Current flowing in the coil is
If ω' = 100 × 2π then ω'L = 40Ω
Current flowing in the coil is
Energy in a current carrying coil is stored in theform of [1988]- a)electric field
- b)magnetic field
- c)dielectric strength
- d)heat
Correct answer is option 'B'. Can you explain this answer?
Energy in a current carrying coil is stored in theform of [1988]
a)
electric field
b)
magnetic field
c)
dielectric strength
d)
heat
|
Shivani Rane answered |
Energy stored in a coil = 
where, L is the self-inductance and i the
current flowing through the inductor. Thus,
energy is stored in the magnetic field of the
coil.
current flowing through the inductor. Thus,
energy is stored in the magnetic field of the
coil.
In the given circuit the reading of voltmeter V1 and V2 are 300 volts each. The reading of the voltmeter V3 and ammeter A are
respectively [2010]
- a)150 V, 2.2 A
- b)220 V, 2.2 A
- c)200 V, 2.0 A
- d)100 V, 2.0 A
Correct answer is option 'B'. Can you explain this answer?
In the given circuit the reading of voltmeter V1 and V2 are 300 volts each. The reading of the voltmeter V3 and ammeter A are
respectively [2010]
respectively [2010]
a)
150 V, 2.2 A
b)
220 V, 2.2 A
c)
200 V, 2.0 A
d)
100 V, 2.0 A
|
Priyanka Iyer answered |
As VL = VC = 300 V, resonance will take
place
∴ VR = 220 V
Current, I =220/100 = 2.2A
∴ reading of V3 = 220 V
and reading of A = 2.2 A
place
∴ VR = 220 V
Current, I =220/100 = 2.2A
∴ reading of V3 = 220 V
and reading of A = 2.2 A
A capacitor has capacity C and reactance X. Ifcapacitance and frequency become double, thenreactance will be [2001]- a)4X
- b)X/2
- c)X/4
- d)2X
Correct answer is option 'C'. Can you explain this answer?
A capacitor has capacity C and reactance X. Ifcapacitance and frequency become double, thenreactance will be [2001]
a)
4X
b)
X/2
c)
X/4
d)
2X
|
Ankita Datta answered |
Capacitive Reactance
Capacitive Reactance (Xc) is the opposition offered by the capacitor to the flow of current through it and is given by the formula:
Xc = 1/ (2πfC)
where f is the frequency of the alternating current and C is the capacitance of the capacitor.
Doubling of Capacitance and Frequency
If the capacitance and frequency of the circuit are doubled, then the new values of capacitance and frequency will be 2C and 2f respectively.
New Reactance
The new reactance (Xnew) can be calculated by substituting the new values of capacitance and frequency in the formula for capacitive reactance:
Xnew = 1/ (2π x 2f x 2C)
Xnew = 1/ (4πfC)
Comparing old and new reactance
Xnew/Xc = (1/4πfC)/(1/2πfC)
Xnew/Xc = 1/2
Xnew = Xc/2
Therefore, if capacitance and frequency become double, then the reactance will be half its original value. The correct option is (b) X/2.
Capacitive Reactance (Xc) is the opposition offered by the capacitor to the flow of current through it and is given by the formula:
Xc = 1/ (2πfC)
where f is the frequency of the alternating current and C is the capacitance of the capacitor.
Doubling of Capacitance and Frequency
If the capacitance and frequency of the circuit are doubled, then the new values of capacitance and frequency will be 2C and 2f respectively.
New Reactance
The new reactance (Xnew) can be calculated by substituting the new values of capacitance and frequency in the formula for capacitive reactance:
Xnew = 1/ (2π x 2f x 2C)
Xnew = 1/ (4πfC)
Comparing old and new reactance
Xnew/Xc = (1/4πfC)/(1/2πfC)
Xnew/Xc = 1/2
Xnew = Xc/2
Therefore, if capacitance and frequency become double, then the reactance will be half its original value. The correct option is (b) X/2.
The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. Theprimary is connected to an A.C. supply of 20 V,50 Hz. The secondary will have an output of [1997]- a)2 V, 5 Hz
- b)200 V, 500 Hz
- c)2V, 50 Hz
- d)200 V, 50 Hz
Correct answer is option 'D'. Can you explain this answer?
The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. Theprimary is connected to an A.C. supply of 20 V,50 Hz. The secondary will have an output of [1997]
a)
2 V, 5 Hz
b)
200 V, 500 Hz
c)
2V, 50 Hz
d)
200 V, 50 Hz
|
|
Shalini Saha answered |
The transformer converts A.C. high voltage
into A.C. low voltage, but it does not cause
any change in frequency. The formula for
voltage is
into A.C. low voltage, but it does not cause
any change in frequency. The formula for
voltage is
Thus, output has voltage 200 V and
frequency 50 Hz.
frequency 50 Hz.
In an electrical circuit R, L, C and an a.c. voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage the current in the circuit is π/3. If instead, C is removed from the circuit, the phase difference is again π/3. The power factor of the circuit is : [2012]- a)1/2
- b)1/√2
- c)1
- d)√3/2
Correct answer is option 'C'. Can you explain this answer?
In an electrical circuit R, L, C and an a.c. voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage the current in the circuit is π/3. If instead, C is removed from the circuit, the phase difference is again π/3. The power factor of the circuit is : [2012]
a)
1/2
b)
1/√2
c)
1
d)
√3/2
|
Shruti Chauhan answered |
when C is remove from the circuit
In an experiment, 200 V A.C. is applied at theends of an LCR circuit. The circuit consists ofan inductive reactance (XL ) = 50 Ω, capacitivereactance (XC ) = 50 Ω and ohmic resistance (R)= 10 Ω. The impedance of the circuit is[1996]- a)10Ω
- b)20Ω
- c)30Ω
- d)40Ω
Correct answer is option 'A'. Can you explain this answer?
In an experiment, 200 V A.C. is applied at theends of an LCR circuit. The circuit consists ofan inductive reactance (XL ) = 50 Ω, capacitivereactance (XC ) = 50 Ω and ohmic resistance (R)= 10 Ω. The impedance of the circuit is[1996]
a)
10Ω
b)
20Ω
c)
30Ω
d)
40Ω
|
|
Diya Datta answered |
Given : Supply voltage (Vac) = 200 V
Inductive reactance (XL) = 50 Ω
Capacitive reactance (XC) = 50 Ω
Ohmic resistance (R) = 10 Ω.
We know that impedance of the LCR circuit
Inductive reactance (XL) = 50 Ω
Capacitive reactance (XC) = 50 Ω
Ohmic resistance (R) = 10 Ω.
We know that impedance of the LCR circuit
An LCR series circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of [1994]- a)π
- b)π/2
- c)π/4
- d)0
Correct answer is option 'D'. Can you explain this answer?
An LCR series circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of [1994]
a)
π
b)
π/2
c)
π/4
d)
0
|
|
Shruti Chauhan answered |
At resonance, 
The circuit
behaves as if it contains R only. So, phase
difference = 0
At resonance, impedance is minimum Zmin =
R and current is maximum, given by
The circuitbehaves as if it contains R only. So, phase
difference = 0
At resonance, impedance is minimum Zmin =
R and current is maximum, given by
It is interesting to note that before resonance
the current leads the applied emf, at
resonance it is in phase, and after resonance
it lags behind the emf. LCR series circuit is
also called as acceptor circuit and parallel
LCR circuit is called rejector circuit.
the current leads the applied emf, at
resonance it is in phase, and after resonance
it lags behind the emf. LCR series circuit is
also called as acceptor circuit and parallel
LCR circuit is called rejector circuit.
A coil of 40 henry inductance is connected inseries with a resistance of 8 ohm and thecombination is joined to the terminals of a 2 voltbattery. The time constant of the circuit is [2004]- a)20 seconds
- b)5 seconds
- c)1/5 seconds
- d)40 seconds
Correct answer is option 'B'. Can you explain this answer?
A coil of 40 henry inductance is connected inseries with a resistance of 8 ohm and thecombination is joined to the terminals of a 2 voltbattery. The time constant of the circuit is [2004]
a)
20 seconds
b)
5 seconds
c)
1/5 seconds
d)
40 seconds
|
Rajesh Chatterjee answered |
Given:
Inductance of coil, L = 40 H
Resistance, R = 8Ω
Battery voltage, V = 2V
Time constant, τ = ?
Formula used:
Time constant of RL circuit = L/R
Calculation:
Time constant, τ = L/R = 40/8 = 5 seconds
Therefore, the correct option is (b) 5 seconds.
Inductance of coil, L = 40 H
Resistance, R = 8Ω
Battery voltage, V = 2V
Time constant, τ = ?
Formula used:
Time constant of RL circuit = L/R
Calculation:
Time constant, τ = L/R = 40/8 = 5 seconds
Therefore, the correct option is (b) 5 seconds.
A step-up transformer operates on a 230 V lineand supplies a load of 2 ampere. The ratio of theprimary and secondary windings is 1 : 25. Thecurrent in the primary is [1998]- a)25 A
- b)50 A
- c)15 A
- d)12.5 A
Correct answer is option 'B'. Can you explain this answer?
A step-up transformer operates on a 230 V lineand supplies a load of 2 ampere. The ratio of theprimary and secondary windings is 1 : 25. Thecurrent in the primary is [1998]
a)
25 A
b)
50 A
c)
15 A
d)
12.5 A
|
Gowri Menon answered |
Given data:
Primary voltage (V1) = 230 V
Secondary current (I2) = 2 A
Turns ratio (N2/N1) = 25
We know that,
V1/V2 = N1/N2 (Voltage ratio equation)
Substituting the given values,
230/V2 = 1/25
V2 = 230 x 25 = 5750 V
We also know that,
I1/I2 = N2/N1 (Current ratio equation)
Substituting the given values,
I1/2 = 25/1
I1 = 50 A
Therefore, the current in the primary is 50 A.
Primary voltage (V1) = 230 V
Secondary current (I2) = 2 A
Turns ratio (N2/N1) = 25
We know that,
V1/V2 = N1/N2 (Voltage ratio equation)
Substituting the given values,
230/V2 = 1/25
V2 = 230 x 25 = 5750 V
We also know that,
I1/I2 = N2/N1 (Current ratio equation)
Substituting the given values,
I1/2 = 25/1
I1 = 50 A
Therefore, the current in the primary is 50 A.
The primary of a transformer when connected toa dc battery of 10 volt draws a current of 1 mA.The number of turns of the primary andsecondary windings are 50 and 100 respectively.The voltage in the secondary and the currentdrawn by the circuit in the secondary arerespectively [NEET Kar. 2013]- a)20 V and 0.5 mA
- b)20 V and 2.0 mA
- c)10 V and 0.5 mA
- d)Zero and therefore no current
Correct answer is option 'D'. Can you explain this answer?
The primary of a transformer when connected toa dc battery of 10 volt draws a current of 1 mA.The number of turns of the primary andsecondary windings are 50 and 100 respectively.The voltage in the secondary and the currentdrawn by the circuit in the secondary arerespectively [NEET Kar. 2013]
a)
20 V and 0.5 mA
b)
20 V and 2.0 mA
c)
10 V and 0.5 mA
d)
Zero and therefore no current
|
|
Shruti Chauhan answered |
A transformer is essentially an AC device.
DC source so no mutual induction between
coils
⇒ E2 = 0 and I2 = 0
DC source so no mutual induction between
coils
⇒ E2 = 0 and I2 = 0
What is the value of inductance L for which the current is maximum in a series LCR circuit with C = 10 μF and ω = 1000s -1 ? [2007]- a)1 mH
- b)cannot be calculated unless R is known
- c)10 mH
- d)100 mH
Correct answer is option 'D'. Can you explain this answer?
What is the value of inductance L for which the current is maximum in a series LCR circuit with C = 10 μF and ω = 1000s -1 ? [2007]
a)
1 mH
b)
cannot be calculated unless R is known
c)
10 mH
d)
100 mH
|
Pooja Choudhary answered |
Condition for which the current is maximum
in a series LCR circuit is,
in a series LCR circuit is,
= L = 100 mH
The primary and secondary coil of a transformerhave 50 and 1500 turns respectively. If themagnetic flux φ linked with the primary coil isgiven by φ= φ0 + 4t, where φ is in webers, t is timein seconds and φ0 is a constant, the outputvoltage across the secondary coil is [2007]- a)120 volts
- b)220 volts
- c)30 volts
- d)90 volts
Correct answer is option 'A'. Can you explain this answer?
The primary and secondary coil of a transformerhave 50 and 1500 turns respectively. If themagnetic flux φ linked with the primary coil isgiven by φ= φ0 + 4t, where φ is in webers, t is timein seconds and φ0 is a constant, the outputvoltage across the secondary coil is [2007]
a)
120 volts
b)
220 volts
c)
30 volts
d)
90 volts
|
Nayanika Reddy answered |
Where
Ns = No. of turns across primary coil = 50
Np = No. of turns across secondary coil
= 1500
Ns = No. of turns across primary coil = 50
Np = No. of turns across secondary coil
= 1500
In an A.C. circuit with voltage V and current I the power dissipated is [1997] - a) dependent on the phase between V and I
- b)
- c)
- d)VI
Correct answer is option 'A'. Can you explain this answer?
In an A.C. circuit with voltage V and current I the power dissipated is [1997]
a)
dependent on the phase between V and I
b)
c)
d)
VI
|
Ritika Khanna answered |
Power dissipated = Erms. Irms = (Erms) (Irms)
cos θ
Hence, power dissipated depends upon
phase difference.
cos θ
Hence, power dissipated depends upon
phase difference.
An ac voltage is applied to a resistance R and aninductor L in series. If R and the inductivereactance are both equal to 3Ω, the phasedifference between the applied voltage and thecurrent in the circuit is [2011]- a)π/6
- b)π/4
- c)π/2
- d)zero
Correct answer is option 'B'. Can you explain this answer?
An ac voltage is applied to a resistance R and aninductor L in series. If R and the inductivereactance are both equal to 3Ω, the phasedifference between the applied voltage and thecurrent in the circuit is [2011]
a)
π/6
b)
π/4
c)
π/2
d)
zero
|
|
Diya Datta answered |
The phase difference φ is given by
The instantaneous values of alternating current and voltages in a circuit are given as
The average power in Watts consumed in the circuit is : [2012M]- a)1/4
- b)√3/4
- c)1/2
- d)1/8
Correct answer is option 'D'. Can you explain this answer?
The instantaneous values of alternating current and voltages in a circuit are given as
The average power in Watts consumed in the circuit is : [2012M]
a)
1/4
b)
√3/4
c)
1/2
d)
1/8
|
Shanaya Rane answered |
The average power in the circuit where cos
φ = power factory
φ = power factory
< P > = Vrms × Irms cos φ
φ = π/3 = phase difference =180/3 = 60
φ = π/3 = phase difference =180/3 = 60
The core of a transformer is laminated because [2006]- a)the weight of the transformer may bereduced
- b)rusting of the core may be prevented
- c)ratio of voltage in primary and secondarymay be increased
- d)energy losses due to eddy currents may beminimised
Correct answer is option 'D'. Can you explain this answer?
The core of a transformer is laminated because [2006]
a)
the weight of the transformer may bereduced
b)
rusting of the core may be prevented
c)
ratio of voltage in primary and secondarymay be increased
d)
energy losses due to eddy currents may beminimised
|
|
Diya Datta answered |
When there is change of flux in the core of a
transformer due to change in current around
it, eddy current is produced. The direction
of this current is opposite to the current
which produces it, so it will reduce the main
current. We laminate the core so that flux is
reduced resulting in the reduced production
of eddy current.
transformer due to change in current around
it, eddy current is produced. The direction
of this current is opposite to the current
which produces it, so it will reduce the main
current. We laminate the core so that flux is
reduced resulting in the reduced production
of eddy current.
Power dissipated in an LCR series circuit connected to an a.c source of emf εε is [2009]- a)
- b)
- c)
- d)
Correct answer is option 'D'. Can you explain this answer?
Power dissipated in an LCR series circuit connected to an a.c source of emf εε is [2009]
a)
b)
c)
d)
|
Snehal Shah answered |
Power dissipated in series LCR;
is called the impedance of the circuit.
A 220 volts input is supplied to a transformer.The output circuit draws a current of 2.0 ampereat 440 volts. If the efficiency of the transformeris 80%, the current drawn by the primarywindings of the transformer is [2010]- a)3.6 ampere
- b)2.8 ampere
- c)2.5 ampere
- d)5.0 ampere
Correct answer is option 'D'. Can you explain this answer?
A 220 volts input is supplied to a transformer.The output circuit draws a current of 2.0 ampereat 440 volts. If the efficiency of the transformeris 80%, the current drawn by the primarywindings of the transformer is [2010]
a)
3.6 ampere
b)
2.8 ampere
c)
2.5 ampere
d)
5.0 ampere
|
|
Nayanika Dasgupta answered |
In a series resonant circuit, having L, C and R as its elements, the resonant current is i. The power dissipated in the circuit at resonance is [2002]- a)
- b)zero
- c)i2ωL
- d)i2R
Correct answer is option 'D'. Can you explain this answer?
In a series resonant circuit, having L, C and R as its elements, the resonant current is i. The power dissipated in the circuit at resonance is [2002]
a)
b)
zero
c)
i2ωL
d)
i2R
|
|
Pooja Choudhary answered |
At resonance 
Current through circuit i =E/R
Power dissipated at Resonance = i2R
Power dissipated at Resonance = i2R
In an a.c circuit the e.m.f. (e) and the current (i) at any instant are given respectively by
e = E0 sin ωt [2008]
i = I0 sin (ωt –φ)
The average power in the circuit over one cycle of a.c. is- a)
- b)
- c)
- d)E0I0
Correct answer is option 'C'. Can you explain this answer?
In an a.c circuit the e.m.f. (e) and the current (i) at any instant are given respectively by
e = E0 sin ωt [2008]
i = I0 sin (ωt –φ)
The average power in the circuit over one cycle of a.c. is
e = E0 sin ωt [2008]
i = I0 sin (ωt –φ)
The average power in the circuit over one cycle of a.c. is
a)
b)
c)
d)
E0I0
|
Arnab Iyer answered |
The average power in the circuit over one
cycle of a.c. is given by
cycle of a.c. is given by
A coil of self-inductance L is connected in serieswith a bulb B and an AC source. Brightness ofthe bulb decreases when [NEET 2013]- a)number of turns in the coil is reduced
- b)a capacitance of reactance XC = XL isincluded in the same circuit
- c)an iron rod is inserted in the coil
- d)frequency of the AC source is decreased
Correct answer is option 'C'. Can you explain this answer?
A coil of self-inductance L is connected in serieswith a bulb B and an AC source. Brightness ofthe bulb decreases when
[NEET 2013]
a)
number of turns in the coil is reduced
b)
a capacitance of reactance XC = XL isincluded in the same circuit
c)
an iron rod is inserted in the coil
d)
frequency of the AC source is decreased
|
|
Diya Datta answered |
By inserting iron rod in the coil,
In the circuit of Fig, the bulb will become suddenly bright if [1989]
- a)contact is made or broken
- b)contact is made
- c)contact is broken
- d)won't become bright at all
Correct answer is option 'C'. Can you explain this answer?
In the circuit of Fig, the bulb will become suddenly bright if [1989]
a)
contact is made or broken
b)
contact is made
c)
contact is broken
d)
won't become bright at all
|
Naveen Menon answered |
When a circuit is broken, the induced e.m.f.
is largest. So the answer is (c).
is largest. So the answer is (c).
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 [2005]
- a)
- b)
- c)
- d)
Correct answer is option 'B'. Can you explain this answer?
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 [2005]
a)
b)
c)
d)
|
Priyanka Sharma answered |
ϕ being the angle by which the current leads the voltage.Given, ϕ=45o
A transistor-oscillator using a resonant circuitwith an inductor L (of negligible resistance) anda capacitor C in series produce oscillations offrequency f. If L is doubled and C is changed to4C, the frequency will be [2006]- a)8f
- b)f / 2 √2
- c)f/2
- d)f/4
Correct answer is option 'B'. Can you explain this answer?
A transistor-oscillator using a resonant circuitwith an inductor L (of negligible resistance) anda capacitor C in series produce oscillations offrequency f. If L is doubled and C is changed to4C, the frequency will be [2006]
a)
8f
b)
f / 2 √2
c)
f/2
d)
f/4
|
|
Lekshmi Banerjee answered |
We know that frequency of electrical
oscillation in L.C. circuit is
oscillation in L.C. circuit is
Eddy currents are produced when [1988]- a)a metal is kept in varying magnetic field
- b)a metal is kept in steady magnetic field
- c)a circular coil is placed in a magnetic field
- d)through a circular coil, current is passed
Correct answer is option 'A'. Can you explain this answer?
Eddy currents are produced when [1988]
a)
a metal is kept in varying magnetic field
b)
a metal is kept in steady magnetic field
c)
a circular coil is placed in a magnetic field
d)
through a circular coil, current is passed
|
Prisha Singh answered |
Eddy currents are produced when a metal is
kept in a varying magnetic field.
kept in a varying magnetic field.
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