As plane-polarised light with amplitude $a$ passes through a polarising filter, as illustrated, the amplitude of the transmitted light becomes $a\cos\theta$. The intensity of the original beam is $I$. What is the intensity of the transmitted light when $\theta$ is $60.0^{\circ}$?
- A$0.250I$
- B$0.500I$
- C$0.750I$
- D$0.866I$