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CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 15 - MCQExams.com

The equation of an alternating voltage is V=220sin[ωt+π6] and the equation for current is I=10sin(ωt+π6). The impedance (in ohm) of the circuit is
  • 11
  • 44
  • 20
  • 22
Find the resonant frequency and Qfactor of a series LCR circuit with L=3.0 H,C=27μF and R=7.4Ω.
  • 111 rad/s,45
  • 111 rad/s,90
  • 55.5 rad/s,45
  • 55.5 rad/s,90
In an inductor, the current l varies with time t as i=5A+16 (A/s) t. If induced emf in the inductor is 5 mV, the self inductance of the inductor is 
  • 3.75×103H
  • 3.75×104H
  • 3.125×103H
  • 3.125×104H
A magnet is moving towards the coil  along the axis and the emf induced tin the coil is 'e' if the coil also starts moving towards the magent with same speed.  the induced emf will be 
  • e2
  • e
  • 2e
  • 4e
A condenser of capacity C is charged to a potential difference of V1. The plates of the condenser are then connected to an ideal inductor of inductance L. The current through the inductors when then potential difference across the condenser reduces to V2
  • C(V21V22)L
  • C(V21+V22)L
  • (C(V21V22)L)1/2
  • (av1v2p2L)1/2
For an alternating current of frequency 5πHz in LCR series circuit with L1H,C1μFR100Ω impedance is :-
  • 100Ω
  • 100πΩ
  • 1002πΩ
  • 100zΩ
yf the frequency of the source e.m.f. in an AC circuit is n , the power varies wath a frequency 
  • n
  • 2n
  • n/2
  • zero
For a series LCR circuit at resonance, the statement which  is not true:-
  • Peak energy stored by a capacitor = peak
    energy stored by an inductor
  • Average power = apparent power
  • Wattless current is zero
  • Power factor is one
An alternating source of frequency ν is connected to a series LCR-circuit. The graph that best represents the variation of the current I with the frequency of the applied ac is
Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be
1452523_be7c533c658344f699a0fc6e277d286b.png
  • maximum in situation (a)
  • maximum in situation (b)
  • maximum in situation (c)
  • the same in all situation
An LCR circuit as shown in the figure is connected to a voltage soruce Vac whose frequency one be varied.
The frequency, at which the voltage across the resistor is maximum, is :
1441369_1db689a2f4ed4a1789dfa78107043116.png
  • 902Hz
  • 143Hz
  • 23Hz
  • 345Hz
As the frequency of an alternating current increases, the impedance of the circuit
  • increase continuously
  • decreases continuously
  • remains constant
  • None of these
Two inductors L1 and L2 are connected in parallel and a time varying current i flows as shown. The ratio of currents i1/i2 at any time t is
1547027_92b37b6b62554fdf86b1bacd3ef59f58.png
  • L1/L2
  • L2/L1
  • L21(L1+L2)2
  • L22(L1+L2)2
In a  RLC  series circuit shown, the readings of voltmeters  V1  and  V2  are  100V  and  120V.  Choose the correct statement  (s). 
1544598_50360299e49a4034a0969c46e834061a.png
  • Voltage across resistor, inductor and capacitor are 50V,86.6V and 206.6V respectively.
  • Voltage across resistor, inductor and capacitor are 10V,90V and 30V respectively.
  • Power factor of the circuit is 513
  • None of these
The resistance of a coil for dc is 10 ohm. When ac is sent through it, its resistance would be
  • A=10ohm
  • A<10ohm
  • A>10ohm
  • A=5ohm
On decreasing the angular frequency of A.C. source used in LCR series circuit, the capacitive reactance____________ and inductive reactance _________ respectively.
  • Increases, Decreases
  • Increases, Increases
  • Decreases, Increases
  • Decreases, Decreases
Two long straight wires equal cross-sectional radii a are located parallel to each other in air .The distance between their axes equal b. Find the mutual capacitance of the wire per unit length under the condition b>>a
  • C=2πε0ln(b/a)
  • C=πε0ln(a/b)
  • C=π/ε0In(b/a)
  • None of these
An alternating emf is applied across a parallel combination of a resistance  R,  capacitance  C  and an inductance  L.  If  IR,IL,IC  are the currents through  R,   L   and  C,  respectively, then the diagram which correctly represents, the phase relationship among  IR,IL,IC  and source emf  E,  is given by
The equation P of an ac is represented by I=0.6 sin 100 πt. The frequency of ac is
  • 50π
  • 50
  • 100π
  • 100
In a series LCR circuit R=200Ω and the voltage and the frequency of the main supply is 220 V and 50 Hz respectively. On talking out the capacities from the circuit the current lags behind the voltage by 30 On taking out the induct or from the circuit the current leads the voltage by 30 The power dissipated in the LCR circuit is  
  • 305 W
  • 210 W
  • 0 W
  • 242 W
In an A.C circuit, a resistance of R ohm is connected in series with an indutance L.If phase angle between voltage and current be450, the value of inductive reacatance  will be  
  • R/4
  • R/2
  • R
  • R/5
The average power of A.C. lost per cycle is given by?
  • 12E0i0sinϕ
  • 12E0i0cosϕ
  • 12E0i0tanϕ
  • 12E0i0ϕ

In the R-C series A.C. circuit, current is by δ than voltage. 

  • ahead,Whereδ=tan1(1ωCR)
  • behind,Whereδ=tan1(1ωCR)
  • ahead,Whereδ=tan1(ωCR)
  • behind,Whereδ=tan1(ωCR)
A choke coil is preferred over a resistor in ac circuit because 
  • it is cheaper than a resistor
  • it lasts longer than a resistor
  • the resistor may over heat and melt
  • it brings about a voltage drop with negligible power consumption
The resonance frequency of a certain RLC series circuit is ωo. A source of angular frequency  2ωo is inserted into the circuit.After transients die out, the angular frequency of current oscillation is
  • ωo2
  • ωo
  • 2ωo
  • 1.5ωo
An A.C. circuit consists of a resistance and a choke in series. The resistance is of 220 Ω and choke is of 0.7 henry. The power absorbed from 220 volts and 50 Hz, source connected with the circuit, is?
  • 120.08 watt
  • 109.97 watt
  • 100.08 watt
  • 98.08 watt
In the circuit diagram shown, Xc=100Ω, XL=200Ω and R=100Ω. The effective current through the source is
1578634_302d2bdf56a34b79bd0c37f108ab1a15.png
  • 2A
  • 2 A
  • 0.5 A
  • 22 A
An ac source of frequency ω when fed into an RC series circuit, current is recorded to be I. If now frequency is charged to ω3 (keeping voltage same) the circuit is found to be I/2.The ration of reactance to resistance at original frequency ω is
  • 2
  • 12
  • 12
  • 3\5
The growth of current in two series LR circuits A and B is shown in C. Let L1,R1 and R2 be the corresponding inductor, resistor values in the two circuits. Then
1567994_4ce77f6ddd804970be8ebfd2c9f6d879.1567994-Q
  • R1>R2
  • R1=R2
  • L1>L2
  • L1<L2
In a series LCR circuit which is connected to an AC voltage source, choose the incorrect statement 
  • Algebraic sum of instantaneous voltage across L,C,R is a variable
  • VLinst+VCinst+VRinst=Vsourceinst
  • Voltage across inductor, capacitor, resistance behave as a vector
  • Current is same in inductor, capacitor and resistance
In fig. 10.43, which voltmeter reads zero, when ω is equal to the resonant frequency of series LCR circuit : 
1574769_7f07e1165b7e442f9e2c74d3b57ac8ea.png
  • V1
  • V2
  • V3
  • None of these
In the series LCR circuit (Fig. 7.33)  , the voltmeter and ammeter readings are : 
1749340_e68fae2d7e284ebda42d20aa8f3b8678.jpg
  • V=100V,I=2A
  • V=100V,I=5A
  • V=1000V,I=2A
  • V=300V,I=1A
In an AC series circuit, the instantaneous current is zero when the instantaneous voltage is maximum. Connected to the source may be a 
  • pure inductor
  • pure capacitor
  • pure resistor
  • combination of an inductor and a capacitor
In the series LCR circuit, the voltmeter and ammeter readings are respectively.
1705013_d6e426adabca488c8df19264bf2fe561.png
  • V=250V,I=4A
  • V=150V,I=2A
  • V=1000V,I=5A
  • V=100V,I=2A
The alternating current is given by the equation i=10sin(100πt+π6). The current attains its first maximum at t is :
  • 1600s
  • 150s
  • 1100s
  • 1300s
In a radio receiver, the short wave and medium wave station are tuned by using the same capacitor but coils of difference inductance Ls and Lm respectively then 
  • Ls>Lm
  • Ls<Lm
  • Ls=Lm
  • None of these
How can you decrease current in an alternating current circuit without any loss of power?
  • By using pure inductor
  • By using pure resistance
  • By using resistance and inductor
  • By using resistance and capacitor
In an A.C. circuit, a resistance of 3Ω, an inductance coil of 4Ω and a condenser of 8Ω are connected in series with an A.C. source of 50 volts (R.M.S). The average power loss in the circuit will be
  • 600 watt
  • 500 watt
  • 400 watt
  • 300 watt
In an LCR series circuit , at resonance
  • the current and voltage are in phase
  • the impedance is maximum
  • the current is minimum
  • the quality factor is independent of R
  • the current leads the voltage by π2
0:0:2


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Practice Class 12 Medical Physics Quiz Questions and Answers