Chapter .
13 AC Circuits
1) The average emf during a positive half cycle of an AC main supply of 220 V
will be
(A) 198 volt
(B) 220 volt
(C) 240 volt
(D) 220√2 volt
2) The maximum charge on the capacitor in an oscillating LC circuit is Q.
The charge on capacitor when the energy is stored equally between
electric and magnetic field is :
(A) Q/4
(B) Q/√3
(C) Q/√2
(D) Q/2
3) If the maximum energy is stored in capacitor at t = 0 then find the
time after which current in the circuit will be maximum.
(A) π/2 ms
(B) π/4 ms
(C) 3.14ms
(D) 2ms
4)In the given circuit, the phase difference between
voltages across R and C is
(A) zero
(B) π/2
(C) π
(D) 3π/2
5) current is found by dividing the area enclosed by the half
cycle by the length of the base of the half cycle.
(A) RMS current
(B) Average current
(C) Instantaneous current
(D) Total current
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6) For a resistor there is phase difference between instantaneous
alternating current and instantaneous alternating emf.
(A) zero
(B) 90°
(C) 180°
(D) 270°
7)Identify the correct statement for
the given circuit.
(A) The current is in phase with the voltage.
(B) The current is out of phase with the voltage.
(C) The current leads the voltage by 90°.
(D) The current lags voltage by 90°.
8) The power factor in a non-inductive circuit is
(A) 0
(B) 1
(C) 2
(D) infinite
9) The average power over a complete cycle in a pure inductive circuit is
(A) 0
(B) 1
(C) 2
(D) Infinite
10) An electric bulb operates 10 V d.c. If this bulb is connected to an a.c.
source and gives
normal brightness, then peak value of the source is .......
a) 141.4 V
b) 14.14 V
c) 1.414 V
d) 0.1414 V
11) A parallel LC resonant circuit is used as ....
a) a tunning circuit in a television receiver set.
b) a transformer
c) a rectifier
d) a filter circuit.
12) In a series LCR AC circuit, the current is maximum when the
impedance is equal to
(A) The reactance
(B) The resistance
(C) twice the reactance
(D) twice the resistance
13) Identify correct relation for Q factor.
(A) Q factor = Resonant frequency + Bandwidth
(B) Q factor = Resonant frequency - Bandwidth
(C) Q factor = Resonant frequency × Bandwidth
(D) Q factor = Resonant frequency ÷ Bandwidth
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14) The reciprocal of impedance in an AC circuit is known as
(A) conductance
(B) inductance
(C) admittance
(D) capacitance
15) The SI unit of admittance is
(A) ohm
(B) siemens
(C) volts
(D) hertz
16) A complex current wave is given as I = (5 + 5sin100 πt)A. Its average
value over one time period is given as is
(A) 10 A
(B) 5 A
(C) √50A
(D) 20 A
17) The average value of sin Ɵ from 0° to 180° is
(A) 0
(B) 0.5
(C) 0.673
(D) 1
18) At resonance, the phase angle in an LCR alternating current circuit is
and the power output is at maximum.
(A) a maximum
(B) zero
(C) 90°
(D) 30°
19) Which of the following statement is true for a series LCR circuit
when inductive and capacitive reactance’s are equal?
(A) The voltage and current are in phase.
(B) The voltage leads current by 90°.
(C) The voltage lags current by 90°.
(D) The voltage leads current by 180°.
20) If A.C. voltage is applied to a pure capacitor, then voltage across the
capacitor
(A) Leads the current by phase angle 90°
(B) Leads the current by phase angle 180°
(C) Lags behind the current by phase angle 90°
(D) Lags behind the current by phase angle 180°
24 The diagram below shows the variation of voltage and current in an AC
) circuit. The circuit contains
(A) Only a resistor.
(B) Only a capacitor.
(C) Only a pure inductor.
(D) A capacitor and an inductor.
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25) In a circuit L, C & R are connected in series with an alternating
voltage of frequency f. the current leads the voltage by 45°. The value of
C is
(A) 0.607
(B) 0.707
(C) 0.808
(D) 1
26) Which of the following converts AC to DC?
(A) Fan
(B) Air conditioner
(C) Computer
(D) Induction heater
27) The length of the phasor represents the value of the quantity.
(A) maximum
(B) minimum
(C) average
(D) rms
28) The average value of AC is the average of all values of the voltage (or
current) over one cycle.
(A) complete
(B) quarter
(C) third
(D) half
29) Which of the following is not possible in an alternating current circuit
(one complete cycle)?
(A) The average value of current is zero
(B) The average value of square of current is zero
(C) Average power dissipation is zero
(D) The phase difference between voltage and current is zero
30) Which of the following behave similarly for an AC and DC circuit?
(A) Capacitor
(B) Inductor
(C) Resistor
(D) Transistor
31) The minimum value of alternating voltages and current can be
(A) Zero
(B) One
(C) rms value
(D) peak value
32) The average power dissipated in a series LCR circuit depends on the
(A) rms value of current only
(B) rms value of current and voltage both
(C) rms value of current and the power factor
(D) rms value of current, voltage and the power factor
33) Identify the SI unit of inductive reactance.
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(A) Volt
(B) Ohm
(C) Joule
(D) Hertz
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