Two polarising filters are set side by side with their planes aligned parallel. The transmission axis of the first polarising filter makes an angle of $50^{\circ}$ with the vertical, while the transmission axis of the second polarising filter makes an angle of $20^{\circ}$ with the vertical. Hence, the angle separating the transmission axes of the two polarising filters is $30^{\circ}$. A beam of vertically polarised light with intensity $8.0\,\text{W m}^{-2}$ is directed normally at the first polarising filter. What intensity of light emerges from the second polarising filter?
- Azero
- B$2.5\,\text{W m}^{-2}$
- C$2.9\,\text{W m}^{-2}$
- D$6.0\,\text{W m}^{-2}$