1

Give reason : The
alternating waveform is called as sinusoidal waveform.


Sinusoidal waveform
 The induced emf in the coil varies with the sine
function of the time angle ωt therefore the alternating waveform is called as
sinusoidal waveform.

2

Explain the
following terms : Waveform , Amplitude
and Frequency


Waveform
 The shape of the
instantaneous value of alternating quantity ( voltage or current ) is
represented on Y – axis and time on X – axis is called waveform of the
alternating quantity.
Amplitude
 The maximum ( Positive
or Negative ) value of an alternating quantity is called as amplitude.
Frequency ( f )
 The numbers of
cycle per second of an alternating quantity is called as frequency.
 Its unit is cycle
per second or Hertz ( Hz ).

3

Explain the
following terms : Cycle , Instantaneous value and Time period


Cycle
 One complete set of
positive and negative cycle of an alternating quantity is called as cycle.
Instantaneous value
 The value of
alternating quantity at given instant (or time) is called as instantaneous
value.
Time period (T)
 It is defined as
the time required to complete one cycle of an alternating quantity.
 It is measured in second.

4

Explain the
following terms : Peak value , Average or mean value , Effective or RMS value
and Form factor


Peak Value
 The maximum value
of positive or negative half cycle of symmetrical waveform of an alternating
quantity is called as peak value.
Average or mean value
 It is DC quantity which
transfers the same charge in a given circuit as is transferred by the
alternating quantity during the same time.
Effective or RMS value
 The RMS value of an
alternating quantity is defined as the value of direct current which when
flowing through a given circuit for a given time produces the same heat as
that is produced by alternating quantity when flowing through the same
circuit for the same time.
Form factor ( K_{f })
 It is defined as
the ratio of the RMS value to the average value of an alternating quantity.
Form factor = RMS
value / Average value
 The value of form
factor for sinusoidal alternating quantity is 1.11

5

Explain the term :
Complex waveform


Complex Waveform
 It is composed of
fundamental waveform and number of other harmonics waveform.

6

What is frequency
of the fundamental harmonic?


50 Hz

7

At which condition,
the complex waveform does not contain distortion?


Distortion in the Complex waveform
 When the two halves of the
complex wave are identical in shape there is no distortion in the output
waveform. It is only possible when only odd harmonics ( 3^{rd }, 5^{th}
, 7^{th} etc ) are present.
 When
the two halves of the complex wave are not identical in shape, there is
distortion in the output waveform. It is only possible when only even
harmonics ( 2^{nd} , 4^{th} , 6^{th} etc ) are
present.

8

State the frequency
of the 5th harmonics if the fundamental frequency 50 Hz?


The frequency of the 5^{th} harmonics is 250 Hz.

9

State the speed of
the 5th harmonics if the fundamental waveform rotates at Ns RPM.


The speed of the 5^{th} harmonics is N_{s} / 5 RPM.

10

State other name of
the RMS current.


Effective / virtual current

11

Which method is
used to find out RMS value of the alternating quantity?


Method to find out RMS quantity
 Mid – ordinate method
 Analytical method

12

State the average
value of the complete symmetrical alternating voltage.


Zero

13

Write the equation
of the RMS voltage, average voltage and form factor for sinusoidal and half
wave rectified voltage


Sinusoidal voltage
 RMS voltage : I_{m} / √ 2
 Average
voltage : 2I_{m} / π
 Form factor : 1.11
Half wave rectified voltage
 RMS voltage : I_{m}
/ 2
 Average
voltage : I_{m} / π
 Form
factor : 1.57

14

Describe the
importance of the amplitude or crest factor.


Importance of amplitude factor
 The dielectric stress on
the insulation depends upon maximum voltage therefore the amplitude factor
is importance during testing of dielectric insulation.
 The iron loss depends upon
maximum flux density not RMS flux density therefore the amplitude factor
greatly affect the value of the iron loss.

15

Why alternating
supply is not used for charging batteries?


The alternating supply
consists of both positive and negative half cycle therefore the charging of
battery is done during positive half cycle and it will discharge during
negative half cycle.

16

State the RMS and
average value of symmetrical rectangular waveform.


The RMS value and
average value of symmetrical rectangular waveform is one.

17

An alternating
current of peak value is 50.0 Amp. If this current is passing through ( a )
Moving coil ammeter ( b ) Moving iron ammeter. What is indication on these
meters?


 The Moving coil
ammeter indicates average value of an alternating quantity. Therefore the
meter indicates Zero reading
for sinusoidal alternating current of peak value 50.0 amps.
 The moving iron
ammeter indicates RMS value of an alternating quantity.
 Therefore the meter
indicates = RMS value of current = 0.707 × Maximum value of current = 0.707 × 50 = 35.35 Amp

18

Which parameters
affect the value of self inductance or back emf of the inductive coil?


The self inductance
of the inductive coil is affected by
 Rate of change of
current and
 Inductance of the
coil : E = – L ( di / dt )

19

Give reason : The
power loss in the pure resistive circuit never becomes zero.


The instantaneous
value of voltage and current are always either either negative or both
positive therefore the power loss never becomes zero.

20

Explain : Pure
inductive coil


Pure inductive coil
 It is coil in which no ohmic resistance and no power
loss. It is only consider for theory point of view.
 Practically the pure inductance
is not possible.

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