Source $S$ produces microwaves at a steady amplitude. The microwaves travel to a metal screen $P$ and are reflected. A stationary wave is set up between $S$ and $P$. The wavelength of the microwaves is much smaller than the separation between $S$ and $P$. A detector $Q$ is then moved from $S$ to $P$ at a slow, constant speed. What happens to the amplitude of the signal detected by $Q$?
- Adecreases steadily
- Bincreases and decreases regularly
- Cincreases steadily
- Dremains constant