In the figure below, P and Q are two equally intense coherent...

$\Delta{P}_{A} = \dfrac{\pi}{2} \times \dfrac{20}{2\pi} - 5 = 0\text{so}\Delta{ϕ}_{A} = 0$

$\Delta{P}_{B} = \dfrac{\pi}{2} \times \dfrac{20}{2\pi} = 5\text{so}\Delta{ϕ}_{B} = \dfrac{\pi}{2}$

$\Delta{P}_{C} = 5 + 5 = 10\text{so} ∆ ϕc = \pi$

$I = {locos}^{2}\dfrac{\Deltaϕ}{2}$

so ${I}_{A} = {I}_{0}$

${I}_{B} = \dfrac{{I}_{0}}{2}$

$\text{Ic} = 0$

so $\text{IA}: {I}_{B}: {I}_{C} = 2: 1: 0$