A student carries out an investigation into microwave polarisation. The microwaves emitted by the transmitter are vertically polarised. If a metal grille is inserted between the microwave transmitter and the receiver, it behaves as a polarising filter. The voltmeter reading is proportional to the intensity of microwaves that pass through the grille. With the grille’s transmission axis vertical, the voltmeter shows $3.50\,\text{V}$. The grille is then turned through an angle $\theta$. The new voltmeter reading is $2.20\,\text{V}$. Determine $\theta$.
- A$37.5^\circ$
- B$39.0^\circ$
- C$51.0^\circ$
- D$52.5^\circ$