Unpolarized light of intensity $I$ is incident on a system of two polarizers, $\mathrm{A}$ followed by $\mathrm{B}$. The intensity of emergent light is $\frac{I}{2}$ . If a third polarizer $\mathrm{C}$ is placed between $\mathrm{A}$ and $\mathrm{B}$ the intensity of emergent light is reduced to $\frac{I}{3}$ . The angle between the polarizers $\mathrm{A}$ and $\mathrm{C}$ is $\theta$ , then