Given below are two statements:
Statement I: Voltage and current in an ac circuit are vector quantities, because they are represented by rotating phasors.
Statement II: In a phasor diagram, the phasors rotate clockwise about the origin with angular speed \(\omega\).
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Both Statement I and Statement II are incorrect.
A phasor is a vector that rotates about the origin with angular speed \( \omega \). Its length gives the peak value, and its projection on the vertical axis gives the value of the voltage or current at that instant.
Statement I Voltage and current in an ac circuit are vector quantities, because they are represented by rotating phasors. — False. Voltage and current are scalar quantities. Phasors are only a simple way to add them. Their amplitudes and phases combine in the same way as the projections of rotating vectors.
Statement II In a phasor diagram, the phasors rotate clockwise about the origin with angular speed \( \omega \). — False. The phasors are taken to rotate counter-clockwise. As they turn, their vertical projections give \( v_m\sin\omega t \) and \( i_m\sin\omega t \).
NCERT (2026-27):
Points to Ponder – “6. Though in a phasor diagram, voltage and current are represented by vectors, these quantities are not really vectors themselves. They are scalar quantities. …”
AC Voltage Applied to a Capacitor – “… Here the current phasor I is π/2 ahead of the voltage phasor V as they rotate counterclockwise. …”