Physics Quiz 2
Chapter 7 Alternating Current
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In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
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1 point
remains same
doubled
halved
zero
Reciprocal of impedance is
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1 point
susceptance
conductance
admittance
transconductance
The peak value of ac voltage on a 220 V mains is
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1 point
200√2 V
300√2 V
220√2 V
210√2 V
In an a.c. generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency ω in a magnetic field B the maximum value of emf generated in the coil is
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1 point
NABR
NABω
NABRω
NAB
A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
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1 point
30%
50%
90%
10%
What is the value of inductance L for which the current is maximum in a series LCR- circuit with C = 10 μF and ω = 1000 s-1?
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1 point
100 mH
1 mH
10 mH
cannot be calculated unless R is known
The reactance of a capacitor C is X. If both the frequency and capacitance be doubled, then new reactance will be
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1 point
X
2X
X/2
X/4
A transformer works on the principle of
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1 point
EMI
SELF INDUCTION
MUTUAL INDUCTION
CONVERTER
Average power generated in an inductor connected to an a.c. source is
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1 point
1/2 LI²
1/2 CV
ZERO
LI²
At resonance frequency the impedance in series LCR circuit is
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1 point
INFINITY
MAXIMUM
MINIMUM
ZERO
If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1/300 seconds after its value becomes zero is
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1 point
5√2 A
5√3/2 A
5/6 A
5√2A
An inductor of reactance 1 Ω and a resistor of 2 Ω are connected in series to the terminals of a 6 V (rms) a.c. source. The power dissipated in the circuit is
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1 point
8 W
12 W
18 W
14.4 W
Average value of ac over a complete cycle _________ .
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1 point
1
0.5
0.67
0
What effect on Inductive reactance with increases in frequency of ac?
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1 point
Remain Same
Decreases
Increases
First increases then decreases
The value of alternating current at any given instant is
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1 point
a maximum value
a peak value
an instantaneous value
a r.m.s value
The main reason for preferring usage of AC voltage over DC voltage is
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1 point
DC Batteries are of low voltage
there are no DC generators
DC uses alternators whereas AC uses generators
AC voltages can be easily and efficiently converted by means of transformers
Alternating current is so called because
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1 point
Voltage alternates between 10 V and 15 V
Current is switched on and off alternately
Voltage alternates between 0 V and 5 V
Polarity alternates from + to – and – to + with time
The rms current Irms is related to the peak current Io
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1 point
Irms = 0.5 Io
Irms = 0.787 Io
Irms = 0.707 Io
Irms = 0.9 Io
Alternating current cannot be measured by D.C. ammeter because,
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1 point
A.C. is virtual
A.C. changes its direction
A.C. cannot pass through D.C. ammeter
Average value of A.C. for complete cycle is zero
If an LCR series circuit is connected to A.C. source then at resonance voltage across
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1 point
R is zero
R equals the applied voltage
C is zero
C equals the applied voltage
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