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CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 14 - MCQExams.com

For the circuit shown in the figure the current through the inductor is 1.6 A , while the current through the condenser is 0.4 A, then the current l drawn from the source is :
1110199_7c6f96e79e3146839aa95849a5b2af87.png
  • 22 A
  • 1.65 A
  • 1.2 A
  • 2.0 A
A pure inductor I, a cpacitory C and a resistance R are connected across a battery of emf E and internal resistance r as shown in figure. Switch Sw is closed at t=0, select the correct alternative(s).
1105369_041d72398555422ab68bd70332ddeed7.PNG
  • current through resistance R is zero all the time
  • current through resistance R is zero at t=0 and t
  • maximum charge stored in the capacitor is CE
  • maximum energy stored in the inductor is equal to the maximum energy stored in the capacitor
In the given AC circuit
1105698_3f5ad13f6c1c4821a221538f2ac954f6.png
  • current I2 and V are is same phase
  • current I2 leads I1 by 900
  • current I leads I2 by θ<900
  • current I leads I1 by θ<900
A LC circuit is in the state of resonance. if C=0.1 μF and L=0.25 henry.  Neglecting ohmic resistance of circuit what is the frequency of oscillations
  • 1007 Hz
  • 100 Hz
  • 109 Hz
  • 500 Hz
An alternating current of 1.5mA and angular frequency 300 rad/sec flows through a 10KΩ resistor and a 0.50μF capacitor in series. find the rms voltage across the capacitor and impedance of the circuit?
  • 1.2×104Ω; 10V
  • 104Ω; 104V
  • 1.0×1.04Ω; 50V
  • 10Ω;10v
A bulb is rated 55W/110V. It is to be connected to a 220V/50Hz with inductor in series. The value inductance, so that bulb gets correct voltage is: 
  • 220ω1
  • 110ω1
  • 377.5ω1
  • 300ω1
Impedance of given circuit is Given: R=1 Ω,C=522π×102 F,L=140π H, frequency of A.C. source = 100 Hz.
1220614_818d9cbd8500425783175d6595fa389f.jpg
  • 1 Ω
  • 2 Ω
  • 2 Ω
  • 22 Ω
An inductance of (200/π) mH, a capacitance of (103/π)F and a resistance of 10 Ω are connected in series with an a.c source 220 v,50 Hz. The phase angle of the circuit is
  • π/6
  • π/4
  • π/2
  • π/3
In a series resonant R-L-C circuit, if L is increased by 25% and C is decreased by 20%, then the resonant frequency will :
  • Increases by 10%
  • Decreases by 10%
  • Remain unchanged
  • Increases by 2.5%
Calculate the capacitive reactance of a condenser in order to run a bulb rated at 10 watt 60 volt when connected in series to an a.c. source of 100 volt.
  • 100Ω
  • 360Ω
  • 600Ω
  • 480Ω
The phase difference between current and voltage in an AC circuit is π/4 radian. If the frequency of AC is 50Hz, then the phase difference is equivalent to the time difference -  
  • 0.78s
  • 15.7ms
  • 0.25s
  • 2.5ms
In a series L-R circuit, connected with a sinusoidal ac source, the maximum potential difference across L and R are respectively 3 volts and 4 volts.
At an instant the potential difference across resistor is 2 volts, across the inductor at the same instant will be:
  • 6
  • 3 cos 30
  • 3 cos 60
  • 6 sec 45
An inductor coil stores U energy when I current is passed through it and dissipates energy at the rate of P. The time constant of the circuit, when this coil is connected across a battery of zero internal resistance is
  • 4UP
  • UP
  • 2UP
  • 2PU
The time constant of a circle is 10sec. When 10 Ω resistance is connected in a series, then constant of a circuit is now 2 sec. Self-inductance of circuit will be
  • 2.5H
  • 5H
  • 15H
  • 25H
A L-C circuit (inductance 0.01 H, capacity 1μF) is connected to a variable frequency ac source. If frequency varies from 1 kHz to 2  kHz, then frequency at which the current in LC circuit is zero is at
  • 1.2 kHz
  • 1.4 kHz
  • 1.6 kHz
  • 1.8 kHz
What is the r.m.s. value of an alternating current which when passed through a resistor produces head which is thrice of that produced by a direct current of 2 amperes in the same resistor:-
  • 6 amp
  • 2 amp
  • 3.46 amp
  • 0.66 amp
Impedence of L-R circuit is
  • R2+w2L2
  • R+wL
  • R+wL
  • R2+w2L2
In an A.C. circuit, a resistance R=40 Ω and an inductance L are connected in series. If the phase angle between voltage and current is 45o, then the value of the  inductive reactance will be
  • 20 Ω
  • 40 Ω
  • 10 Ω
  • 50 Ω
A series R LC circuit has a bandwidth of 300rad/sec at a resonance frequency of 3000rad/sec when excited by voltage  source of 100V. The inductance of coil is 0.1H the value of R and voltage across C are respectively.
  • 10Ωand1000V
  • 30Ωand100V
  • 30Ωand1000V
  • 300Ωand1000V
In LC parallel circuit L=10 mH and C=9μF. What is the frequency if inductive reactance is equal to capacities reactance?  
  • 5.3 kHz
  • 0.53 kHz
  • 53 kHz
  • 50 kHz
A coil has reactance of 100Ω when the frequency is 50Hz. If the frequency becomes 150Hz, then the reactance will be
  • 100Ω
  • 300Ω
  • 450Ω
  • 600Ω
In the following circuit the emf source is E0=200 volt, R=20Ω, L = 0.1 henry. C = 10.6 farad and frequency is variable then the current at frequency f = 0 and f = is
1284054_d9be57ad7b5e4b96aa702e7e6e72c62a.GIF
  • Zero, 10 A
  • 10 A, zero
  • 10 A, 10 A
  • Zero, zero
In the given circuit,VCE =30 V, VBB =20 V, RB 1 M Ω ,RC 10 K Ω Neglecting vBE  and taking β 50, the values of IC  and IE are respectively 
1289178_13f2ed40d46a4a45bce420e11430eeac.jpg
  • 1mA,1.02mA
  • 2mA,2.02mA
  • 10mA,1mA
  • 2mA,0.99mA
For a series RLC circuit R=XL=2XC. The impedance of the circuit and phase difference (between) V and i will be
  • 5R2,tan1(2)
  • 5R2,tan1(12)
  • 5XC,tan1(2)
  • 5R,tan1(12)
A direct current of 10 A is superimposed on an alternating current l=40cosωt(A) flowing through a wire. The effective value of the resulting current will be 
  • 102A
  • 202A
  • 203A
  • 30 A
A student connects a long air cored coil of manganin wire to a 100VD.C. supply and records a current of 25amp. When the same coil is connected across 100V.50za.c. the current reduces to 20A, the reactance of the coil is:-
  • 4Ω
  • 3Ω
  • 5Ω
  • None
The most appropriate I-H curve for a paramagnetic substance is:
1321308_79fca804ec6746c98765ec69fb950964.PNG
  • OA
  • OB
  • OC
  • OD
Alternating current is given by i = (3 sin ω t + 4 cos ω t)A  the rms current will be
  • 72 A
  • 12 A
  • 52 A
  • 32 A
If the power factor changes from 12 to 14 then the increase in impedance in AC circuit with constant resistance is
  • 20%
  • 50%
  • 25%
  • 100%
In the given circuit R is a resistor. L is an inductor and B1 and B2 are two bulbs and initially the switch S was closed. If the switch S is turned off. Then 
1330037_0f765b3f65b842a2934359908b9fe605.png
  • Both B1 and B2 die out promptly
  • Both B1 and B2 die out with some delay
  • B1 die out promptly but B2 with some delay
  • B2 die out promptly but B1 with some delay
From the figure shown, a series L-C-R circuit connected to a variable frequency 200V source. L=5H,C=80μF and R=40Ω. Then the source frequency which drives the circuit at resonance is
1318617_1413a87514524af8bb041489dba6534d.PNG
  • 25Hz
  • 25πHz
  • 50Hz
  • 50πHz
An inductor (XL=2Ω) a capacitor (Xc=8Ω) and a resistance (8Ω) are connected in series with an ac source. The voltage output of A.C source is given by v=10 cos 100 πt. The instantaneous p.s. between A and B, when it is half of the voltage output from source at that instant will be:
1302362_938c7e7801eb4fc397e9ab0b2271abca.png
  • 247volts
  • 245volts
  • 724volts
  • 524volts
A 50Hz alternating current of peak value 1 ampere flows through the primary coil of a transformer. If the mutual inductance between the primary and secondary be 1.5 henry, then the mean value of the induced voltage is:
  • 75 volt
  • 150 volt
  • 225 volt
  • 300 volt
In a series LCR circuit K = 200 S2 and the voltage and frequency of the main supply are 220 V and 50 Hz respectively. On taking out the capacitor from the circuit, the current leads the voltage byOn taking out the indicator from the circuit the current leads the voltage byThe power dissipated in the LCR circuit is :

  • 342 W
  • 305 K
  • 209 K
  • 242 K
In the circuit shown in figure. the a.c. source gives a voltage V = 20 cos(200π+1) The reading of vulimeter and amineter will be
1339394_d8f5e3ad5d904c2a8d819d4d7201b5da.png
  • 0V,0.47A
  • 5.6V,1.4A
  • 0V,1.4A
  • 2R(2μ1)
The power factor of a circuit in which a box having unknown electrical devices connected in series with a resistor of resistance 3Ω is 3/5. The reactance  of the box is
  • 5Ω
  • 53ω
  • 4Ω
  • 43ω
The time taken by an ac of 50 Hz in reaching from zero to its rms value is 
  • 20 ms
  • 10 ms
  • 5 ms
  • 2.5 ms
If resonant frequency of a R-L-C circuit is Δω, then which of the following quantity is regarded as a measure of the sharpness of resonance?
  • ω0Δω
  • ω02Δω
  • 2ω0Δω
  • ω02ω
The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?
  • R alone
  • RL
  • LC
  • L alone
An alternating current is given by
i=i1cosωt+i2sinωt. The rms current is given by:
  • i1+i22
  • |i1+i2|2
  • i21+i222
  • i1+i22
The tuned collector oscillator circuit used in the local oscillator of a radius receiver makes use of a tuned circuit with L=60μH and C=400pF.
Calculate the frequency of oscillations
  • 1.03KHz
  • 1.03Hz
  • 1.03GHz
  • 1.03MHz
Current through an AC series circuit is 4 A if operated at resonant frequency ωo/2. current reduces to 2 . A then at 2ωo. current in the :  
  • 2A
  • 1A
  • 2A
  • 3A
Growth of current in two different L-R circuit are depicted by the I-t graphs shown. Angle subtended by the curves with time axis at time t=0 are also shown in the graph τ1 and τ2 are time constants for the circuits 1 and 2 respectively. Choose the CORRECT alternative
1347954_fb421deae51c406f82ce2f2f4551d094.png
  • τ1τ2=23
  • τ1τ2=32
  • Initial rate of change of current for circuit-2 is 2 times that of circuit-1
  • Initial rate of change of current for circuit-2 is 4 times that of circuit-1
In an AC circuit instantaneous current is given by i=i0sinπ6t. The time from starting when current in circuit becomes equal to its rms value for the first time is 
  • 1.5s
  • 2s
  • 2.5s
  • 3s
A potential difference of 6V is applied to a coil of inductance 0.5 H and a resistance of 4 ohm connected in series. The time taken for the current to reach half is maximum value is (in seconds).
  • loge28
  • loge24
  • loge48
  • loge84
In a series resonant LCR circuit, the voltage across R is 100V and R= 1kΩ with C =2μF.The resonant frequency ω is 200 rad/s . At resonance the voltage across L is:
  • 25×102V
  • 40 V
  • 250 V
  • 4×103V
The effective resistance between A and B in the given circuit is 
1388937_d7d6c76e127a4da59741eff8ed4bda67.PNG
  • 2Ω
  • 7Ω
  • 3Ω
  • 6Ω
The current (i) in the inductance is varying with according to the plot shown in figure.
Which one of the following is the correct variation of voltage with time in the coil?
1402221_33c616c57c6345f181fe367c5cd2df77.png
A coil of induction 0.5 H is connected to a 18 V battery. The rate of growth of current in the inductor, just after the switch S is closed.
1402025_d61d0b50d4cb46eba97b3f161b58be59.png
  • Zero
  • 18 A/s
  • 36 A/s
  • Infinite
Which of the following combinations should be selected for better tunning of an LCR circuit used for communication
  • R=20Ω,L= =1.5H,C=35μ
  • R=25Ω L=2.5H,C=45μF
  • R=15Ω,L=3.5H,C=30μF
  • R=25Ω,L =1.5H,C= 45 μF
0:0:2


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