JEE Questions for Physics Alternating Current Quiz 2 - MCQExams.com

In the circuit shown in Fig, the bulb B will become suddenly bright when
Physics-Alternating Current-61376.png
  • Contact is made or broken
  • Contact is made
  • Contact is broken
  • Won’t become bright at all
When a sheet of metal is placed in a magnetic field, which changes from zero to a maximum value, the induced current are set up in the direction shown in Fig. what is the direction of magnetic field ?
Physics-Alternating Current-61377.png
  • into the plane of the paper
  • out of the plane of the paper
  • west to east
  • south to north
An aeroplane in which the distance between the tips of the wings is 50 m is flying horizontally with a speed of 360 km/h over a place where the vertical component of earth’s magnetic field is 2×10-4 Wb/m2. The potential difference between the tips of the wings would be
  • 0.1 V
  • 1.0 V
  • 0.2 V
  • 0.01 V
In Fig. final value of current in 10Ω resistor, when plug of key K is inserted is
Physics-Alternating Current-61379.png

  • Physics-Alternating Current-61380.png
  • 2)
    Physics-Alternating Current-61381.png

  • Physics-Alternating Current-61382.png
  • zero
Fig. represents a primitive motor. A metal wire slides on a horse shoe shaped metal loop of width 0.25m. These have negligible resistance, but there is a 1.0Ω resistor in the circuit as well as a 6.0 V battery. There is uniform magnetic field directed in the plane of the page of magnitude 0.5 T. A force of 0.25 N to the left is required to keep it moving with constant speed to the right, then current flowing is
Physics-Alternating Current-61383.png
  • 2 × 10-3 A
  • 0.2 A
  • 2 A
  • 6 A
A motor armature develops a torque of 100 Nm when it draws 40 A from the line. The torque developed if the armature current is increased to 70 A and the magnetic field strength is reduced to 80% of its initial value is
  • 100 Nm
  • 140 Nm
  • 175 Nm
  • 80 Nm
Fig. shows the variation of voltage and current in an a.c. circuit. The circuit contains
Physics-Alternating Current-61386.png
  • only a capacitor
  • only a pure inductor
  • only a resistor
  • a capacitor and inductor
An alternating voltage of frequency w is applied in electric circuit consisting of the an inductance L and capacitance C, connected in parallel. Then across the inductance coil,
I. Current is maximum
II. Current is minimum,
III. Voltage is minimum
IV. Voltage is maximum,
Make the correct choice
  • (I) & (III) both are correct
  • (I) & (IV) both are correct
  • (II) & (III) both are correct
  • (II) and (IV) both are correct
In a step down transformer, use of 120 V line, provides a pot.diff. of 2400 V. If the primary coil has 75 turns, number of turns in secondary coil is :
  • 150
  • 1500
  • 1200
  • 1575
The best material for the core of a transformer is
  • stainless steel
  • mild steel
  • hard steel
  • soft iron
Alternating current cannot be measured by dc ammeter because
  • ac cannot pass through dc ammeter
  • Average value of complete cycle is zero
  • ac is virtual
  • ac changes its direction
The resistance of a coil for dc is in ohms. In ac, the resistance
  • Will remain same
  • Will increase
  • Will decrease
  • Will be zero
In an ac circuit, peak value of voltage is 423 volts. Its effective voltage is
  • 400 volts
  • 323 volts
  • 300 volts
  • 340 volts
An alternating current of r.m.s. value 10 A is passed through a 12 Ω resistor. The maximum potential difference across the resistor is
  • 20 V
  • 29 V
  • 169.68 V
  • None of these
The frequency of ac mains in India is
  • 30 c/s or Hz
  • 50 c/s or Hz
  • 60 c/s or Hz
  • 120 c/s or Hz

Physics-Alternating Current-61391.png
  • 10 V
  • 2)
    Physics-Alternating Current-61392.png
  • 5 V
  • 1 V
An electric heater rated 220 V and 550 W is connected to A.C. mains. The current drawn by it is
  • 0.8 A
  • 2.5 A
  • 0.4 A
  • 1.25 A
What is the approximate peak value of an alternating current producing four times the heat produced per second by a steady current of 2.0 A in a resistor
  • 2.8 A
  • 4.0 A
  • 5.6 A
  • 8.0 A
The voltage of domestic ac is 220 volt. What does this represent
  • Mean voltage
  • Peak voltage
  • Root mean voltage
  • Root mean square voltage
An alternating voltage e = 200 sin 100 t is applied to a series combination of R = 30 Ω and an inductor of 400 mH.The power factor of the circuit is
  • 0.01
  • 0.2
  • 0.05
  • 0.042
  • 0.6
The process by which ac is converted into dc is known as
  • Purification
  • Amplification
  • Rectification
  • Current amplification
A bulb is connected first with dc and the ac of same voltage it will shine brightly with
  • AC
  • DC
  • Brightness will be in ratio 1/1.4
  • Equally with both
If an ac main supply is given to be 220 V. What would be the average e.m.f. during a positive half cycle
  • 198V
  • 386V
  • 256V
  • None of these
A 280 ohm electric bulb is connected to 200 V electric line. The peak value of current in the bulb will be
  • About one ampere
  • Zero
  • About two ampere
  • About four ampere
If an alternating voltage is represented as E = 141 sin (628 t), then the r.m.s. value of the voltage and the frequency are respectively
  • 141 V, 628 HZ
  • 100 V, 50 Hz
  • 100 V, 100 Hz
  • 141 V, 100 Hz
The maximum value of ac voltage in a circuit is 707 V.Its r.m.s. value is
  • 70.7 V
  • 100 V
  • 500 V
  • 707 V

Physics-Alternating Current-61402.png
  • 70.7 V, 70.7 mA
  • 70.7 V, 70.7A
  • 141.4 V, 141.4 mA
  • 141.4 V, 141.4 A
  • 100 V, 100 mA
Two electric bulbs marked 25W ̶ 220V and 100W - 220V are connected in series to a 440V supply. Which of the bulbs will fuse?
  • Both
  • 100W
  • 25 W
  • Neither
Choke coil works on the principle of
  • Transient current
  • Self induction
  • Mutual induction
  • Wattless current
A choke coil has
  • High inductance and low resistance
  • Low inductance and high resistance
  • High inductance and high resistance
  • Low inductance and low resistance
A resistor and a capacitor are connected in series with an ac source. If the potential drop across the capacitor is 5 V and that across resistor is 12 V, the applied voltage is
  • 13 V
  • 17 V
  • 5 V
  • 12 V
An alternating e.m.f. is applied to purely capacitive circuit. The phase relation between e.m.f. and current flowing in the circuit is or In a circuit containing capacitance only
  • e.m.f. is ahead of current by π/2
  • Current is ahead of e.m.f. by π/2
  • Current lags behind e.m.f. by π
  • Current is ahead of e.m.f. by π
The average power dissipated in a pure inductor of inductance L when an ac current is passing through it, is
(Inductance of the coil L and current I)

  • Physics-Alternating Current-61407.png
  • 2)
    Physics-Alternating Current-61408.png

  • Physics-Alternating Current-61409.png
  • Zero

Physics-Alternating Current-61410.png
  • 1 H
  • 2 H
  • 3 H
  • 0.5 H
An alternating voltage is connected in series with a resistance R and an inductance L. If the potential drop across the resistance is 200V and across the inductance is 150 V, then the applied voltage is
  • 350V
  • 250V
  • 500V
  • 300V
In a circuit containing an inductance of zero resistance, the e.m.f. of the applied ac voltage leads the current by
  • 90o
  • 45o
  • 30o
  • 0o
In a pure inductive circuit or In an ac circuit containing inductance only, the current
  • Leads the e.m.f. by 90°
  • Lags behind the e.m.f. by 90°
  • Sometimes leads and sometime lags behind the e.m.f.
  • Is in phase with the e.m.f.
A 20 volts 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
  • 16 volts
  • 10 volts
  • 8 volts
  • 6 volts
For a series LCR circuit at resonance, the statement which is not true is
  • Wattless current is zero
  • Power factor is zero
  • Peak energy stored by a capacitor = peak energy stored by an inductor
  • Average power = apparent power
The power factor of LCR circuit at resonance is
  • 0.707
  • 1
  • Zero
  • 0.5
An inductance of 1 mH a condenser of 10μF and a resistance of 50Ω are connected in series. The reactances of inductor and condensers are same. The reactance of either of them will be
  • 100Ω
  • 30 Ω
  • 3.2 Ω
  • 10Ω
An ac circuit consists of an inductor of inductance 0.5 H and a capacitor of capacitance 8μF in series. The current in the circuit is maximum when the angular frequency of ac source is
  • 500 rad/sec
  • 2 × 105 rad/sec
  • 4000 rad/sec
  • 5000 rad/sec
In a region of uniform magnetic induction B = 10-2 tesla, a circular coil of radius 30 cm and resistance π2 ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is
  • 4π2 mA
  • 30 mA
  • 6 mA
  • 200 mA
In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 ohm in series. The resonance frequency in per second is
  • 600 radian
  • 600 Hz
  • 500 radian
  • 500 Hz
The impedance of a circuit consists of 3 ohm resistance and 4 ohm reactance. The power factor of the circuit is
  • 0.4
  • 0.6
  • 0.8
  • 1.0
L, C and R denote inductance, capacitance and resistance respectively. Pick out the combination which does not have the dimensions of frequency

  • Physics-Alternating Current-61421.png
  • 2)
    Physics-Alternating Current-61422.png

  • Physics-Alternating Current-61423.png

  • Physics-Alternating Current-61424.png
The power factor of a good choke coil is
  • Nearly zero
  • Exactly zero
  • Nearly one
  • Exactly one
An alternating current source of frequency 100 Hz is joined to a combination of a resistance, a capacitance and a coil in series. The potential difference across the coil, the resistance and the capacitor is 46, 8 and 40 volt respectively. The electromotive force of alternating current source in volt is
  • 94
  • 14
  • 10
  • 76
L, C and R represent physical quantities inductance, capacitance and resistance respectively. The combination representing dimension of frequency is
  • LC
  • 2)
    Physics-Alternating Current-61427.png

  • Physics-Alternating Current-61428.png

  • Physics-Alternating Current-61429.png
In a series circuit R = 300Ω, L = 0.9 H, C = 2.0µF and ω = 1000 rad/sec. The impedance of the circuit is
  • 1300Ω
  • 900Ω
  • 500Ω
  • 400Ω
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