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CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 5 - MCQExams.com

An amplitude modulated (AM) radio operates at 550kHz to 1650kHz. If L is fixed and C is varied for tuning then minimum and maximum value of C is

  • C, 3C
  • C, 6C
  • C, 9C
  • C, 12C
The correct curve representing the variation of capacity reactance Xc with frequency f is
A resistance R and a capacitor C are joined to a source of AC of constant e.m.f and variable frequency. The potential difference across C is V. If the frequency of AC is gradually increased, V will
146787.png
  • increase
  • decrease
  • remain constant
  • first increase and then decrease
A series AC circuit has a resistance of 4Ω and a reactance of 3Ω. The impedance of the circuit is
  • 5Ω
  • 7Ω
  • 12/7Ω
  • 7/12Ω
The natural frequency of a LC circuit is
  • 12πLC
  • 12πCL
  • 12πLC
  • LC
An AC source producing emf E=E0[cos(100πs1)t]+E0cos[(500πs1)t] is connected in series with a capacitor and a resistance, the steady state current in the circuit is found to be i=i1[cos(100πs1)t+φ1]+i2cos[(500πs1)t+φ2]
  • i1>i2
  • i1=i2
  • i1<i2
  • Insufficient information
Which of the following plots may represent the reactance of a series LC combination?
146700_757d6b928edf4635b95c48624b265779.png
  • (a)
  • (b)
  • (c)
  • (d)
In the adjacent circuit diagram, initially switch S is opened and the circuit is in steady state. At time t=0, the switch S is closed and the new steady state is reached. Choose the correct option (s)
1109230_f44695683154456fa10ef2b638a5142a.png
  • Current in the inductor when the circuit reaches the new steady state is 4A.
  • The net change in the magnetic flux in the inductor is 1.5 Wb
  • The potential difference across the inductor is 9 volt when the circuit reaches the new steady state
  • The change stored in the capacitor in the new steady state is 1.2 mC
An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance
  • of the inductor increases
  • of the resistor increases
  • of the capacitor increases
  • of the circuit increases
In an LCR circuit the value of XL,XC and R are 300 Ω, 200 Ω and 100 Ω respectively.The total impedance of the circuit will be
  • 600 Ω
  • 200 Ω
  • 141 Ω
  • 310 Ω
The resultant reactance in an LCR circuit is
  • XL+XC
  • XLXC
  • X2L+X2C
  • X2LX2C
The angular frequency of an AC source is 10 radian/sec. The reactance of 1μF capacitor will be
  • 104Ω
  • 102Ω
  • 101Ω
  • 105Ω
A solenoid of length 10 cm, diameter 1 cm, number of turns 500 with relative permeability of the core 2000, is connected to an ac source of frequency 50 Hz. Then, the reactance is
  • zero
  • 55 Ω
  • 105 Ω
  • 155 Ω
An inductance coil of 1 H and a condenser of capacity 1 pF produce resonance. The resonant frequency will be
  • 106πHz
  • 27π×106Hz
  • 2π106Hz
  • 1062πHz
If the values of L,C and R in a series LCR circuit are 10 mH, 100 μF and 100Ω respectively then the value of resonant frequency will be
  • 1032πHz
  • 2×103Hz
  • 2×103piHz
  • 103Hz
An AC voltmeter in an LCR circuit reads 30 volt across resistance, 80 volt across inductance and 40 volt across capacitance. The value of applied voltage will be
  • 50 Volt
  • 25 Volt
  • 150 Volt
  • 70 Volt
A coil of 10 mH and 10 Ω resistance is connected in parallel to a capacitance of 0.1μF. The impedance of the
  • 102Ω
  • 104Ω
  • 106Ω
  • 108Ω
The reactance of a condenser of capacity 50 μF for an AC of frequency 2×103 Hertz will be
  • 5 ohm
  • 2π
  • 3π
  • 5π
In the following circuit the values of L,C,R and E0 are 0.01 H, 105F,25Ω and 220 volt respectively. The value of current flowing in the circuit at f=0 and f= will respectively be
147460.jpg
  • 8 A and 0 A
  • 0 A and 0 A
  • 8 A and 8 A
  • 0 A and 8 A
The capacitive reactance of a condenser of capacity 25μF for an AC of frequency 4000 Hz will be
  • 5πΩ
  • 10πΩ
  • 5πΩ
  • π5Ω
In the figure two identical bulbs, each with filament resistance 100 Ω are connected to a resistor R=100 Ω, and an inductor (XL=100Ω) as shown in the Figure. Then, which bulb glows more
148278.jpg
  • B1
  • B2
  • both glow equally
  • cannot be predicted
The values of XL,XC and R in an AC circuit are 8 Ω, 6Ω and 10 Ω respectively. The total impedance of the circuit
  • 10.2Ω
  • 12.2Ω
  • 10Ω
  • 24.4Ω
The turning circuit of a radio receiver has a resistance of 50 Ω, 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 π2=10):
  • 2.5 pF
  • 5.0 pF
  • 25 pF
  • 50 pF
The ac generator in the Figure supplies 150 V(max) at 50 Hz. With the switch open as shown in the diagram, the resulting current leads the generator emf by 60. With the switch in position 1, the current lags the generator emf by 30. When the switch is in position 2, the maximum current is 3A. Then, the value of R is:
149398.jpg
  • 50/3Ω
  • 83.3 Ω
  • 133.3Ω
  • 50 Ω
An ideal choke takes a current of 10 Amperes when connected to an ac supply of  125 volt and 50 Hz. A pure resistor under the same condition takes a current of  12.5 Ampere. If the two are connected to an ac supply of 1002 volt and 40 Hz,  then the current in a series combination of the above resistor and inductor is:
  • 10 A
  • 12.5 A
  • 20 A
  • 25 A
For the circuit shown in the Figure, the current through the inductor is 0.9 A while the current through the condenser is 0.4 A
149697.jpg
  • current drawn from generator I = 1.13 A
  • ω=1(1.5LC)
  • I = 0.5 A
  • I = 0.6 A
A broadcasting centre broadcasts at 300 metre band. A capacitor of capacitance 2.5μF is available. The value of the inductance required for resonant circuit is nearly
  • 1×104H
  • 1×108H
  • 1×106H
  • 1×102H
A circuit containing a 80 mH inductor and 60 μF capacitor in series is connected to a 230 V,50 Hz supply. If the resistance in the circuit is negligible then the current amplitude will be
  • 11.63 A
  • 8.23 A
  • 9.2 A
  • 13.67 A
If in a series L-C-R ac circuit, the voltages across L, C and R are V1,V2 and V3 respectively, then the voltage of the source is always
  • equal to V1+V2+V3
  • equal to V1V2+V3
  • more than V1+V2+V3
  • none of the above is true
A high-impedance ac voltmeter is connected in turn across the inductor, the capacitor, and the resistance in a series circuit having an ac source of 100 V(rms) and gives the same reading in volts in each case. Then, this reading is:
  • 100/3 volts
  • 300 volts
  • 100 volts
  • incomplete data
In an ideal parallel LC circuit, the capacitor is charged by connecting it to a D.C. source which is then disconnected. The current in the circuit 
  • Becomes zero instantaneously
  • Grows monotonically
  • Decays monotonically
  • Oscillates instantaneously
An ac source producing emf  e=E0[cos(100πt)+cos(500πt)] is connected in series with a capacitor and a resistor. The steady state current in the circuit is found to be i=I1cos(100πt+φ1)+I2cos(500πt+φ2)
  • I1>I2
  • I1=I2
  • I1<I2
  • nothing can be said
In an electric circuit the applied alternating emf is given by E=100sin(314t) volts and current flowing I=sin(314t+π3), Then, the impedance of the circuit is (in Ω)
  • 1002
  • 100
  • 1002
  • None of the above
A coil of negligible resistance is connected in series with a 90 Ω resistor across a 120 V, 60 Hz line. An ac voltmeter reads 90 V across the resistance, then the inductance of the coil is approximately
  • 0.2 H
  • 0.3 H
  • 0.4 H
  • 0.7 H
In an ac circuit, the resistance of R Ω is connected in series with an inductance I. If phase angle between voltage and current be 45, the value of inductive reactance will be:
  • R/2
  • R/2
  • R
  • Insufficient data
You apply f=12πLC to find L. Which frequency will you select?
  • when VR is minimum
  • when VR is maximum
  • when VC is maximum
  • when VC is minimum
In the circuit shown in fig., the resonant frequency is
206505_6b555722aef04087aabce22638d35e7e.png
  • 200Hz
  • 220Hz
  • 225.08Hz
  • 230Hz
If resistance of 100Ω and the inductance of 0.5 henry and capacitance of 10×106 farad are connected  in series through 50Hz A.C supp;y, then impedence is
  • 1.8765Ω
  • 18.76Ω
  • 187.6Ω
  • 101.3Ω
In which of the following circuit, there may be no change in current with increase in the frequency when same ac current is passed through them:
In an LCR circuit the capacitance is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to
  • L/4
  • L/2
  • 2L
  • 4L
In the given circuit, the current drawn from the source is
206637.PNG
  • 20A
  • 10A
  • 5A
  • 52A
The most stable frequency can be generated using
  • LC series circuit
  • LC parallel circuit
  • crystal oscillator
  • RC phase shift oscillator
With increase in frequency of an ac supply, the impedance of an LCR series circuit
  • remains constant
  • increases
  • decreases
  • decrease at first becomes minimum and then increases.
Two coils A and B are connected in series across a 240 V,50 Hz supply. The resistance of A is 5 Ω and the inductance of B is 0.02 H. The power consumed is 3 kW and the power factor is 0.75. The impedence of the circuit is
  • 0.144 Ω
  • 1.44 Ω
  • 14.4 Ω
  • 144 Ω
In a circuit inductance L and capacitance C are connected as shown in figure. A1 and A2 are ammeters.
When key K is pressed to complete the circuit, then just after closing key (K), the readings of A1 and A2 will be
206663_cb11ea8695084a2cbbc3593eef3c5206.png
  • zero in both A1 and A2
  • maximum in both A1 and A2
  • zero in A1 and maximum in A2
  • maximum in A1 and zero in A2
Capacitance (C) of the capacitor is
  • 10μF
  • 15μF
  • 20μF
  • None of these
An inductive coil has a resistance of 100 Ω. When an a.c. signal of frequency 1000 Hz is fed to the coil, the applied voltage leads the current by 45o. What is the inductance of the coil?
  • 10mH
  • 12mH
  • 16mH
  • 20mH
An alternating voltage of 220V,50Hz frequency is applied across a capacitor of capacitance 2μF. The impedence of the circuit is:
  • π5000
  • 1000π
  • 500π
  • 5000π
The instantaneous voltage through a device of impedence 20Ω is e=80sin100πt. The effective value of the current is
  • 3A
  • 2.828A
  • 1.732A
  • 4A
For watt-less power in an AC circuit the phase angle between the current and voltage is
  • 0o
  • 90o
  • 45o
  • Not possible
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Practice Class 12 Medical Physics Quiz Questions and Answers