A plane-polarised light wave with intensity $I_0$ falls normally on a polarising filter. The intensity of the wave transmitted at first is $0$. A second polarising filter is then placed between the source and the first filter. Its transmission axis makes an angle of $45^\circ$ with the transmission axis of the first filter, as shown. What is the intensity of the wave transmitted by the filter combination?
- A$0$
- B$\frac{I_0}{8}$
- C$\frac{I_0}{4}$
- D$\frac{I_0}{2}$