Assertion and Reason Questions Chapter-7 Alternating Current
Assertion (A) and other labelled Reason (R). Select the correct answer to these
questions from the options as given below.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
1. Assertion (A): Alternating current (AC) changes direction periodically.
Reason (R): AC is defined as a current that reverses its direction
at regular intervals.
2. Assertion (A): The root mean square (RMS) value of an AC current is less than
its peak value.
Reason (R): The RMS value is used to calculate the equivalent DC
value for power in AC circuits.
3. Assertion (A): The frequency of an AC signal determines the number of cycles
it completes in one second.
Reason (R): Frequency is defined as the reciprocal of the time
period of one cycle.
4. Assertion (A): The average value of an AC over a complete cycle is zero.
Reason (R): The positive and negative halves of the AC waveform
cancel each other out.
5. Assertion (A): In an AC circuit, the current and voltage can be out of phase.
Reason (R): This phase difference affects the power factor of the
circuit.
6. Assertion (A): Inductive reactance increases with frequency in an AC circuit.
Reason (R): Inductive reactance is given by the formula \(\ {X_L} = = 2\pi fL\)
7. Assertion (A): Capacitive reactance decreases with increasing frequency in an
AC circuit.
Reason (R): Capacitive reactance is given by the formula
\(\ {X_C} \) = \(\frac{1}{2 \pi fC X} \).
8. Assertion (A): In a series RLC circuit, the total impedance is the vector sum
of resistance, inductive reactance, and capacitive reactance.
Reason (R): Impedance takes into account both resistance and
reactance in AC circuits.
9. Assertion (A): The power factor in an AC circuit is the cosine of the phase
angle between current and voltage.
Reason (R): A power factor of 1 indicates maximum power transfer
in the circuit.
10. Assertion (A): The average power in an AC circuit can be calculated using
the formula P=VIcos
ϕ.
Reason (R): This formula accounts for the phase difference between
voltage and current.
11. Assertion (A): An inductor in an AC circuit behaves like a resistor at high
frequencies.
Reason (R): Inductive reactance increases with frequency, limiting
current flow.
12. Assertion (A): The phase difference in a purely resistive AC circuit is
zero.
Reason (R): In a resistive circuit, the current and voltage are
always in phase.
13. Assertion (A): In a parallel RLC circuit, the total current is the sum of
the individual branch currents.
Reason (R): In parallel circuits, voltage across each component is
the same.
14. Assertion (A): The resonant frequency of a series RLC circuit occurs when
the inductive and capacitive reactances are equal.
Reason (R): At resonance, the circuit behaves as a purely
resistive circuit.
15. Assertion (A): The voltage across an inductor lags the current by 90 degrees
in an AC circuit.
Reason (R): This phase relationship is due to the energy storage
characteristics of inductors.
16. Assertion (A): The total impedance in an AC circuit can be found using the
formula Z =\(\ \sqrt {R^2 + ( {X_L} - {X_C} )^2} \).
Reason (R): This formula accounts for the effects of both
resistance and reactance.
17. Assertion (A): In an AC circuit, the phase angle can affect the amount of
power consumed.
Reason (R): A larger phase angle results in a lower power factor
and less effective power consumption.
18. Assertion (A): The current in a capacitor lags behind the voltage by 90
degrees in an AC circuit.
Reason (R): Capacitors store energy in the electric field, leading
to this phase difference.
19. Assertion (A): The power factor of a circuit can be improved by adding
capacitors in parallel with inductive loads.
Reason (R): Capacitors can compensate for the inductive reactance,
reducing the overall phase angle.
20. Assertion (A): The peak current in an AC circuit is higher than the RMS
current.
Reason (R): The peak current is the maximum value attained by the
current in a cycle.
21. Assertion (A): In a series RLC circuit, at resonance, the impedance is
minimized.
Reason (R): At resonance, the inductive and capacitive reactances
cancel each other out.
22. Assertion (A): A transformer can step up or step down voltage in an AC
circuit.
Reason (R): The transformer operates based on electromagnetic
induction principles.
23. Assertion (A): The energy stored in an inductor is given by the formula
E= \(\frac{1}{2} L I^{2}\) .
Reason (R): This formula indicates that energy storage in an
inductor is proportional to the square of the current.
24. Assertion (A): The impedance of a capacitor in an AC circuit is represented
as a negative imaginary number.
Reason (R): This representation reflects the phase difference
between current and voltage in capacitors.
25. Assertion (A): The inductance of a coil affects its behavior in an AC
circuit.
Reason (R): Inductance determines the amount of reactance that the
coil provides against the AC current.
26. Assertion (A): In a purely resistive AC circuit, the power factor is 1.
Reason (R): This means all the power is used effectively without
any reactive power.
27. Assertion (A): The energy stored in a capacitor is given by E=
\(\frac{1}{2} C V^{2}\).
Reason (R): This formula shows that the energy stored is
proportional to the square of the voltage across the capacitor.
28. Assertion (A): The total power in a three-phase AC circuit can be calculated
using P = \(\ \sqrt{3}\ {V_L} {I_L} \cos \phi \).
Reason (R): This formula accounts for the line voltage and line
current in a three-phase system.
29. Assertion (A): AC motors are generally more efficient than DC motors for
high power applications.
Reason (R): AC motors have fewer maintenance requirements due to
the absence of brushes.
30. Assertion (A): The skin effect causes AC current to flow primarily near the
surface of conductors.
Reason (R): This effect increases with the frequency of the AC
signal.
31. Assertion (A): An RLC circuit can exhibit resonant behavior at certain
frequencies.
Reason (R): At resonance, the circuit can oscillate at its natural
frequency with maximum amplitude.
32. Assertion (A): The current in a series circuit remains the same throughout.
Reason (R): In a series circuit, there is only one path for
current to flow.
33. Assertion (A): The time period of an AC wave is inversely proportional to
its frequency.
Reason (R): The time period is defined as the duration of one
complete cycle of the wave.
34. Assertion (A): AC signals can be represented mathematically as sinusoidal
functions.
Reason (R): Sinusoidal functions provide a smooth and continuous
representation of alternating currents.
35. Assertion (A): The maximum voltage in an AC circuit is referred to as the
peak voltage.
Reason (R): The peak voltage is higher than the RMS voltage.
36. Assertion (A): An alternating current is often used in household electrical
systems.
Reason (R): AC is easily transformed to different voltage levels,
making it suitable for long-distance transmission.
37. Assertion (A): The total current in a parallel circuit is equal to the sum
of the currents through each branch.
Reason (R): This is due to the fact that each branch has the same
voltage across it.
38. Assertion (A): The phase angle in an RLC circuit can be controlled by
varying the resistance, inductance, or capacitance.
Reason (R): Changing any of these parameters affects the reactance
and thus the phase relationship.
39. Assertion (A): The apparent power in an AC circuit is the product of the RMS
voltage and RMS current.
Reason (R): Apparent power does not take into account the phase
difference between current and voltage.
40. Assertion (A): The phase difference in a series RL circuit is always between
0 and 90 degrees.
Reason (R): The presence of resistance prevents the phase
difference from reaching 90 degrees.
41. Assertion (A): In an AC circuit, capacitors can lead the current.
Reason (R): In capacitive circuits, the current reaches its
maximum value before the voltage does.
42. Assertion (A): The energy loss in an AC circuit can be minimized by using
reactive components.
Reason (R): Reactive components store energy temporarily, reducing
energy loss.
43. Assertion (A): In an RLC circuit, the quality factor (Q) indicates the
selectivity of the circuit.
Reason (R): A higher Q factor means the circuit has a narrower
bandwidth.
44. Assertion (A): The back EMF in an inductor opposes the change in current.
Reason (R): This is a result of Lenz's law, which states that
induced EMF opposes the cause of its production.
45. Assertion (A): AC voltages can be rectified to obtain DC voltages.
Reason (R): Rectification processes involve converting alternating
voltage to direct voltage.
46. Assertion (A): In an AC circuit, the power factor can affect the total power
consumed.
Reason (R): A lower power factor indicates that a larger portion
of the current is reactive, which does not perform useful work.
47. Assertion (A): The phase difference in a purely capacitive circuit is 90
degrees.
Reason (R): In a capacitive circuit, the current leads the voltage
by 90 degrees.
48. Assertion (A): The maximum power transfer theorem states that maximum power
is transferred when the load resistance equals the source resistance.
Reason (R): This condition ensures that the voltage drop across
the load is maximized.
49. Assertion (A): The reactance in an AC circuit can be either inductive or
capacitive.
Reason (R): The reactance depends on the type of reactive
component in the circuit.
50. Assertion (A): The resonant frequency of an RLC circuit is determined by the
values of R, L, and C.
Reason (R): The resonant frequency is inversely proportional to
the square root of the inductance and capacitance.