Class 12 Alternating Current CBSE Questions & Answers

Class 12 · Alternating Current

This is Physics Class 12 Alternating Current CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
Domestic power supply in India is
  • A
    24 V DC
  • B
    230 V 50 Hz
    Correct
  • C
    110 V 60 Hz
  • D
    416 V 60 Hz
2
The main reason for preferring use of ac voltage over dc voltage
  • A
    ac voltages can be easily and efficiently converted from one voltage to the other by means of transformers
    Correct
  • B
    There are no DC generators
  • C
    DC uses alternators whereas as uses generators
  • D
    DC Batteries are of low voltage
3
Alternating current is so called because
  • A
    current is supplied alternatively on and off
  • B
    Polarity alternates from + to – and I to + with time
    Correct
  • C
    voltage alternates between 10 V and 15 V
  • D
    voltage alternates between 0 V and 5 V
4
In a Resistance voltage and current are
  • A
    in phase
    Correct
  • B
    out of phase by 120\(^\circ \)
  • C
    out of phase by 90\(^\circ \)
  • D
    out of phase by 180\(^\circ \)
5
If \({{\rm{i}}_{\rm{m}}}\) is the maximum current the average value of power dissipated in a resistance R over a cycle is
  • A
    \(2i_m^2R\)
  • B
    \({1 \over 2}i_m^2R\)
    Correct
  • C
    \({3 \over 2}i_m^2R\)
  • D
    \(i_m^2R\)
6
The rms current I is related to the peak current \({{\rm{i}}_{\rm{m}}}\) by
  • A
    I = 0.787 \({{\rm{i}}_{\rm{m}}}\)
  • B
    I = 0.5 \({{\rm{i}}_{\rm{m}}}\)
  • C
    I = 0.9 \({{\rm{i}}_{\rm{m}}}\)
  • D
    I = 0.707 \({{\rm{i}}_{\rm{m}}}\)
    Correct
7
Effective voltage V is related to peak voltage \({{\rm{v}}_{\rm{p}}}\) by
  • A
    V = 0.5 \({{\rm{v}}_{\rm{p}}}\)
  • B
    V = 0.787 \({{\rm{v}}_{\rm{p}}}\)
  • C
    V = 0.9 \({{\rm{v}}_{\rm{p}}}\)
  • D
    V = 0.707 \({{\rm{v}}_{\rm{p}}}\)
    Correct
8
Phasor diagrams show phasors(vectors)
  • A
    show phases of matter
  • B
    rotating counterclockwise with constant angular speed
    Correct
  • C
    show phase only
  • D
    show the angular speed
9
Average power supplied to an inductor over one complete cycle
  • A
    is 1
  • B
    is zero
    Correct
  • C
    is always positive
  • D
    is always negative
10
In an inductance the current
  • A
    lags the voltage
    Correct
  • B
    leads the voltage
  • C
    builds very fast
  • D
    is in phase
11
Average power supplied to a capacitor over one complete cycle
  • A
    is always positive
  • B
    is 1
  • C
    is zero
    Correct
  • D
    is always negative
12
in a capacitance the current
  • A
    lags the voltage
  • B
    builds very slowly
  • C
    leads the voltage
    Correct
  • D
    is in phase
13
In a series LCR circuit excited with AC applied
  • A
    current in L and R is same but different in C
  • B
    current in L, C and R is the same
    Correct
  • C
    current in L and C is same but different in R
  • D
    current in R and C is same but different in L
14
If \({{\bf{V}}_{\bf{L}}}\), \({{\bf{V}}_{\bf{R}}}\) , \({{\bf{V}}_{\bf{C}}}\), and V represent the voltage across the inductor, resistor, capacitor and the source, respectively, on the phasor diagram
  • A
    \({{\bf{V}}_{\bf{L}}}\) and \({{\bf{V}}_{\bf{R}}}\) are directed opposite to each other and \({{\bf{V}}_{\bf{C}}}\) leads \({{\bf{L}}_{\bf{C}}}\) by 90\(^\circ \)
  • B
    \({{\bf{V}}_{\bf{L}}}\) and \({{\bf{V}}_{\bf{C}}}\) are directed opposite to each other and \({{\bf{V}}_{\bf{R}}}\) leads \({{\bf{V}}_{\bf{C}}}\) by 90\(^\circ \)
    Correct
  • C
    \({{\bf{V}}_{\bf{R}}}\) and \({{\bf{V}}_{\bf{C}}}\) are directed opposite to each other and \({{\bf{V}}_{\bf{R}}}\) leads \({{\bf{V}}_{\bf{C}}}\) by 90\(^\circ \)
  • D
    \({{\bf{V}}_{\bf{L}}}\) and \({{\bf{V}}_{\bf{C}}}\) are at 90\(^\circ \) to each other and \({{\bf{V}}_{\bf{R}}}\) leads \({{\bf{V}}_{\bf{C}}}\) by 90\(^\circ \)
15
If vm and im are peak voltage and current, Impedance Z in an AC circuit is
  • A
    \({{{v_m}} \over {{i_m}}}\)
    Correct
  • B
    \({{{v_m}} \over {2{i_m}}}\)
  • C
    \({{\rm{v}}_{\rm{m}}}{{\rm{i}}_{\rm{m}}}\)
  • D
    \({{2{v_m}} \over {{i_m}}}\)