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Physics M.C.Q [1M]

Alternating Current · Bihar Board (BSEB) STD 12 Science (BSEB - English Medium). 29 questions.

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M.C.Q [1M]

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29 questions · timed · auto-graded

MCQ 11 Mark
Peak value of applied alternating voltage in a LR cir- cuit is 5 V. If magnitude of maximum voltage across the ends of resistor is 3 V. then maximum value of voltage across the inductor is
  • A
    2 V
  • ✓
    4 V
  • C
    $5 \sqrt{2} V$
  • D
    Zero
Answer
Correct option: B.
4 V
(b)4 V
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MCQ 21 Mark
Alternating current cannot be measured by de ammeter because:
  • A
    Alternating current does not pass through ammeter.
  • ✓
    Average value of current for a complete cycle is zero.
  • C
    Some part of alternating current does not pass through ammeter.
  • D
    None of the above
Answer
Correct option: B.
Average value of current for a complete cycle is zero.
(b)Average value of current for a complete cycle is zero.
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MCQ 31 Mark
Frequency and potential difference of AC sent to homes in India is:
  • ✓
    50 Hz, 220 V
  • B
    60 Hz, 220 V
  • C
    60 Hz, 110 V
  • D
    50 Hz, 110 V
Answer
Correct option: A.
50 Hz, 220 V
(a)50 Hz, 220 V
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MCQ 41 Mark
Impedance of a circuit of inductance L and resis- tance R is denoted by:
  • A
    LR
  • B
    $\frac{ L }{ R }$
  • ✓
    $\sqrt{L^2 \omega^2+R^2}$
  • D
    $\sqrt{ R ^2 \omega^2+ L ^2}$
Answer
Correct option: C.
$\sqrt{L^2 \omega^2+R^2}$
(c)$\sqrt{L^2 \omega^2+R^2}$
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MCQ 51 Mark
Magnitude of potential difference across L. C and R in a series LCR circuit is 100 V. If resistor is re- moved, then magnitude of current in the circuit is:
  • A
    Zero
  • ✓
    Infinite
  • C
    10 A
  • D
    20 A
Answer
Correct option: B.
Infinite
(b)Infinite
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MCQ 61 Mark
A pure resistor is joined with a capacitor. The magni- tude of tangent of their phase difference in the cir- cuit is:
  • A
    $C \omega / R$
  • B
    $R / C \omega$
  • ✓
    $1 / C \omega/R$   
  • D
    $C \omega R$
Answer
Correct option: C.
$1 / C \omega/R$   
(c)$1 / C \omega/R$   
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MCQ 71 Mark
Resistance of capacitor for high frequency is:
  • A
    High
  • ✓
    Low
  • C
    Zero
  • D
    None of these
Answer
Correct option: B.
Low
(b)Low
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MCQ 91 Mark
In an ac circuit, potential differenc is $V =10 \cos \omega t$ and current flowing through is $I =2 \sin \omega t$ then magnitude of power dissipated is :
  • ✓
    Zero
  • B
    10 W
  • C
    5 W
  • D
    1.25 W
Answer
Correct option: A.
Zero
(a)Zero
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MCQ 101 Mark
A direct current of 4 A is flowing through any circuit. Root mean square value of the current is:
  • ✓
    4 A
  • B
    $\frac{4}{\sqrt{2}} A$
  • C
    $4 \sqrt{2} A$
  • D
    There is no root mean square value of direct current.
Answer
Correct option: A.
4 A
(a)4 A
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MCQ 111 Mark
An electric bulb is made to work at 12 V dc. When this bulb is joined with an ac source, it gives normal brightness. Peak voltage of ac source is:
  • A
    12 V
  • ✓
    17 V
  • C
    24 V
  • D
    8.4 V
Answer
Correct option: B.
17 V
(b)17 V
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MCQ 121 Mark
Root mean square value of ac voltage $V=$ $200 \sin \left(100 \pi t+\frac{\pi}{2}\right)$ is :
  • ✓
    $100 \sqrt{2} V$
  • B
    $200 \sqrt{2} V$
  • C
    200 V
  • D
    100 V
Answer
Correct option: A.
$100 \sqrt{2} V$
(a)$100 \sqrt{2} V$
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MCQ 131 Mark
Alternating current is produced in:
  • A
    Transformers
  • B
    Choke coil
  • ✓
    Dynamo
  • D
    Battery
Answer
Correct option: C.
Dynamo
(c)Dynamo
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MCQ 141 Mark
L, C and R represent physical quantities-inductance, capacitance and resistance respectively. The one which has same dimensions as time is:
  • A
    $\frac{ C }{ L }$
  • B
    $\frac{1}{ RC }$
  • ✓
    $\frac{ L }{ R }$
  • D
    $\frac{ RL }{ C }$
Answer
Correct option: C.
$\frac{ L }{ R }$
(c)$\frac{ L }{ R }$
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MCQ 151 Mark
Maximum value of voltage in an ac circuit is 282 V. The effective magnitude of voltage is:
  • ✓
    200 V
  • B
    300 V
  • C
    400 V
  • D
    564 V
Answer
Correct option: A.
200 V
(a)200 V
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MCQ 161 Mark
In an ac circuit, current $I=5 \sin \left(100 t-\frac{\pi}{2}\right)$ ampere and altemating potential difference is $V =200$ sin ( 100 t ). The power dissipated in the circuit is :
  • A
    1000 W
  • ✓
    Zero W
  • C
    40 W
  • D
    20 W
Answer
Correct option: B.
Zero W
(b)Zero W
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MCQ 171 Mark
Frequency of electric current in alternating current I $=200 \sin \left(60 \pi t+\frac{\pi}{6}\right)$ is :
  • A
    120 Hz
  • B
    60 Hz
  • C
    90 Hz
  • ✓
    30 Hz
Answer
Correct option: D.
30 Hz
(d)30 Hz
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MCQ 181 Mark
The number of turns in primary and secondary coils of a transformer are 100 and 300 respectively. If in- put power is 60 W, then output power will be:
  • ✓
    60 W
  • B
    20 W
  • C
    180 W
  • D
    None of these
Answer
Correct option: A.
60 W
(a)60 W
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MCQ 191 Mark
A transformer increases ac voltage supply from 220 V to 2200 V. If there are 2000 turns in the second- ary coil, then number of turns in the primary coil is:
  • A
    100
  • B
    50
  • ✓
    200
  • D
    30
Answer
Correct option: C.
200
(c)200
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MCQ 201 Mark
Which of the following substance is most suitable to make core of transformer?
  • ✓
    Soft iron
  • B
    Nickel
  • C
    Copper
  • D
    Stainless steel
Answer
Correct option: A.
Soft iron
(a)Soft iron
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MCQ 211 Mark
Potential difference in ac circuit is $V =20 \sin \omega t$ and current flowing is $I =5 \cos \omega t$, then power dissipated in watts is :
  • B
    10
  • C
    5
  • D
    100
Answer
(a)0
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MCQ 221 Mark
A lamp whose resistance is $280 \Omega$ is joined with an ac source of 200 V . The peak value of current flowing in the lamp is :
  • ✓
    1.0 A
  • B
    2.0 A
  • C
    0.7 A
  • D
    1.4 A
Answer
Correct option: A.
1.0 A
(a)1.0 A
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MCQ 231 Mark
In an ac circuit, phase of current lags the phase of voltage by an angle of $\frac{\pi}{3}$. The component in the circuit is :
  • A
    L and C
  • ✓
    R and I
  • C
    R and C
  • D
    Only R
Answer
Correct option: B.
R and I
(b)R and I
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MCQ 241 Mark
Magnitude of current at half power point in a circuit is:
  • A
    $I _{\max } \sqrt{2}$
  • ✓
    $\frac{I_{\max }}{\sqrt{2}}$
  • C
    $2 I _{\max }$
  • D
    $\frac{I_{\max }}{2}$
Answer
Correct option: B.
$\frac{I_{\max }}{\sqrt{2}}$
(b)$\frac{I_{\max }}{\sqrt{2}}$
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MCQ 251 Mark
Power factor of LCR circuit in resonance is:
  • A
    0
  • B
    0.5
  • ✓
    1
  • D
    Depends on values of L, C and R.
Answer
Correct option: C.
1
(c)1
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MCQ 261 Mark
Resistance of a circuit is $12 \Omega$ and impedance is $15 \Omega$. The power factor of the circuit is :
  • A
    0.4
  • ✓
    0.8
  • C
    0.125
  • D
    1.25
Answer
Correct option: B.
0.8
(b)0.8
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MCQ 271 Mark
Phase difference between voltage across the ends of an inductor coil and capacitor in radians is:
  • ✓
    $\pi$
  • B
    $\frac{\pi}{2}$
  • C
    Zero
  • D
    $2 \pi$
Answer
Correct option: A.
$\pi$
(a)$\pi$
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MCQ 281 Mark
Phase difference between ac current and emf is $\frac{\pi}{2}$.Which of the following cannot be a component of the circuit?
  • A
    L, C
  • B
    Only L
  • C
    Only C
  • ✓
    R, L
Answer
Correct option: D.
R, L
(d)R, L
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MCQ 291 Mark
An electric heater is heated by de and ac respec- tively. The potential difference applied across the ends of heater for both ac and de is same. Heat gener- ated per second will be more:
  • A
    On heating with ac
  • B
    On heating with de
  • ✓
    Same in both
  • D
    None of the above two
Answer
Correct option: C.
Same in both
(c)Same in both
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