Two polarisers P_1 and P_2 are placed in such a way that the...

Two polarisers $P_1$ and $P_2$ are placed in such a way that the intensity of the transmitted light will be zero. A third polariser $P_3$ is inserted in between $P_1$ and $\mathrm{P}_2$, at the particular angle between $\mathrm{P}_2$ and $\mathrm{P}_3$. The transmitted intensity of the light passing the through all three polarisers is maximum. The angle between the polarisers $\mathrm{P}_2$ and $\mathrm{P}_3$ is :