Phasor digrams

  • Phasor diagrams are the diagrams representing alternating current and voltage of same frequency as vectors or phasors with phase angle between them.
  • Phasors are the arrows rotating in the anti-clockwise direction i.e., they are rotating vectors but they represent scalar quantities.
  • Thus alternatinc current and voltage varying sinusoidally can be represented by anticlockwise rotating vectors if they satisfy following conditions
    (i) length of the vector must be equal to the peak value of alternating voltage or current.
    (ii) vector representing alternating current and voltage would be at horizontal position at the instant when alternating quantity is zero.
  • In certain circuits when current reaches its maximum value after emf becomes maximum then current is said to lag behind emf.
  • When current reaches its maximum value before emf reaches its maximum value then current is said ti lead the emf.
  • Figure given below shows the current lagging behind the emf by 90 degree.

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