Phase and Phase Difference

PHASE AND PHASE DIFFERENCE

Consider the two quantities

i₁= I_m sin wt; i₂ = I_msin (wt - ϕ), i₃ = I_m sin (wt + ϕ)

i₁, i₂ is and is are sinusoidal quantities varying with the same peak value and frequency. However i₁, i₂ and is do not reach the maximum and minimum values at the same instant of time. This is clear from figure 3.3 (a). i₂ reaches the maximum only " ϕ " degrees after i₁.

The current i₁ leads i₂ by ϕ degrees or i₂ lags behind i₁ by ϕ. On the other hand, the current i₃ = I_m sin (wt + ϕ) is said to lead i₁ by ϕ degrees. As another example consider V₁ = V_m sin wt and v₂ = V_m2sin wt. These two are in phase as they reach their maximum and minimum values at the same time and of course have the same frequency. It is shown in figure 3.3 (b).